(CNN) The feds are suing Ferguson in a move to force police reform in the city.

"We intend to aggressively prosecute this case," Attorney General Loretta Lynch told reporters Wednesday, "and we intend to prevail."

Authorities had no choice but to file a lawsuit after the Ferguson City Council voted Tuesday to change the terms of a deal negotiators had been hashing out for months, Lynch said.

"The residents of Ferguson have suffered the deprivation of their constitutional rights, the rights guaranteed to all Americans, for decades. They have waited decades for justice," Lynch said. "They should not be forced to wait any longer."

The residents of Ferguson should not be forced to wait any longer. https://t.co/f6SIjOqWq0

The lawsuit alleges a pattern and practice of unconstitutional police conduct in the city.

A city spokesman told CNN that officials will have no comment about the Justice Department's lawsuit until Thursday.

Ferguson officials have not seen the lawsuit, city spokesman Jeff Small said.

Negotiations over reforms to the city's police force and municipal court system began after a Justice Department investigation last year found the Ferguson Police Department had discriminated against African-Americans , targeting them disproportionately for traffic stops, use of force and jail sentences.

"These violations were not only egregious, they were routine. They were encouraged by the city in the interest of raising revenue," Lynch said Wednesday. "They were driven, at least in part, by racial bias and they occurred disproportionately against African American residents of Ferguson."

City officials have said their Tuesday vote wasn't a rejection of a deal with the Justice Department but was rather a push to return to the table and change some of the terms out of concerns over costs.

Lynch said the council knowingly voted against an agreement approved by the city's own negotiators.

"The city was well aware that by deciding not to accept it, they were choosing litigation," she said. "This was their choice."

City Council proposed seven amendments

In a unanimous vote Tuesday night, council members approved the deal -- but only if the Justice Department accepts seven amendments.

The Justice Department wasn't expecting any changes to the negotiated deal and wasted little time in responding.

"The Ferguson City Council has attempted to unilaterally amend the negotiated agreement," Vanita Gupta, head of the agency's Civil Rights Division, said in a statement . "Their vote to do so creates an unnecessary delay in the essential work to bring constitutional policing to the city, and marks an unfortunate outcome for concerned community members and Ferguson police officers."

Photos: Ferguson protests mark a year of outrage Photos: Ferguson protests mark a year of outrage Members of a group calling themselves the "Oath Keepers" appear in Ferguson carrying large guns on Monday, August 10, one day after a police confrontation led to a protester being shot. Sunday, August 9, marked the one-year anniversary of the death of Michael Brown. Hide Caption 1 of 15 Photos: Ferguson protests mark a year of outrage Demonstrators protest in Ferguson on August 10. Hide Caption 2 of 15 Photos: Ferguson protests mark a year of outrage A demonstrator is arrested in Ferguson on August 10. Hide Caption 3 of 15 Photos: Ferguson protests mark a year of outrage Protesters march to the Federal Courthouse on August 10 in St. Louis. Hide Caption 4 of 15 Photos: Ferguson protests mark a year of outrage Cornel West, center, joins other protesters sitting on the steps of the Thomas F. Eagleton Federal Courthouse as members of the Federal Protective Service stand watch August 10 in St. Louis. Protesters have been arrested after blocking the entrance to the courthouse while calling for more aggressive U.S. government response to what they call racist law enforcement practices. Hide Caption 5 of 15 Photos: Ferguson protests mark a year of outrage A man with gunshot wounds lies face down in a parking lot after a shootout with police in Ferguson on Sunday, August 9. Demonstrations started peacefully, but gunfire erupted Sunday night. Police say the man fired at them. Hide Caption 6 of 15 Photos: Ferguson protests mark a year of outrage Police take cover after gunfire in Ferguson on August 9. Hide Caption 7 of 15 Photos: Ferguson protests mark a year of outrage Demonstrators march along West Florissant Avenue in Ferguson on August 9. West Florissant is not far from Canfield Drive, where Brown was shot a year ago. Hide Caption 8 of 15 Photos: Ferguson protests mark a year of outrage A protester yells in front of a line of police in Ferguson on August 9. Hide Caption 9 of 15 Photos: Ferguson protests mark a year of outrage Protesters march in the rain in Ferguson on August 9. Hide Caption 10 of 15 Photos: Ferguson protests mark a year of outrage Demonstrators stage a "die-in" along West Florissant Avenue in Ferguson on August 9. Hide Caption 11 of 15 Photos: Ferguson protests mark a year of outrage Police face off with demonstrators in Ferguson on August 9. Hide Caption 12 of 15 Photos: Ferguson protests mark a year of outrage People attend a memorial service outside Canfield Apartments in Ferguson on August 9. Several hundred demonstrators stood in silence at the spot where Brown was shot and killed. Hide Caption 13 of 15 Photos: Ferguson protests mark a year of outrage Brown supporters wear T-shirts with the late teen's picture and the message "Chosen 4 Change" on August 9 as they take part in the remembrance ceremony in Ferguson. Hide Caption 14 of 15 Photos: Ferguson protests mark a year of outrage People walk past a plaque honoring Brown following the memorial service in Ferguson on August 9. Hide Caption 15 of 15

The national spotlight on Ferguson began after the fatal shooting of 18-year-old Michael Brown by Officer Darren Wilson in August 2014. Brown, who was unarmed, was black, and Wilson is white. Brown's death prompted days of protests and riots in Ferguson and a national conversation about the role of race in police interactions with citizens.

Reaction to the City Council vote was mixed, the St. Louis Post-Dispatch reported

One activist, Debra Kennedy, called the public hearings "a farce, because the DOJ is not going to go back and renegotiate," the newspaper reported. "It was like a 'no' vote."

Others chanted, "You can't amend justice," according to the Post-Dispatch.

Seven months of negotiation

The agreement that City Council wants to change was negotiated over seven months between the city and the Justice Department.

"Although we did not get everything we wanted in the agreement, we certainly made sure that what was agreed upon can be implemented in a timely and sufficient manner," Ferguson Mayor James Knowles III said of the consent decree the city received January 26.

"We're not trying to take away any safeguards," Knowles told CNN affiliate KMOV . "We're not trying to take away anything substantive out of the decree."

City Councilwoman Ella James agreed.

"There are some things in the consent decree that we're asking to be amended, but all in all I think we're moving forward, we're moving in a positive direction," she told CNN affiliate KTVI.

What City Council wants

The original agreement would require the city to hire additional senior staff dedicated to the implementation of the deal and in areas such as crisis intervention and community-police relations. Other costs to the city of Ferguson would include the creation of an electronic complaint tracking system, an early intervention system and training throughout various levels of the police department.

Photos: Unrest in Ferguson Photos: Unrest in Ferguson Police officers walk past the smoldering remains of a beauty supply store in Ferguson, Missouri, on Tuesday, November 25. Ferguson has been struggling to return to normal since Michael Brown, an unarmed black teenager, was killed by Darren Wilson, a white police officer, on August 9. The grand jury did not indict Wilson in the case, prompting new waves of protests in Ferguson and across the country. Hide Caption 1 of 34 Photos: Unrest in Ferguson A woman cleans up glass from a business' shattered window on November 25. Hide Caption 2 of 34 Photos: Unrest in Ferguson A Ferguson firefighter surveys rubble at a strip mall that was set on fire overnight. Hide Caption 3 of 34 Photos: Unrest in Ferguson Protesters run away after police deployed tear gas in Ferguson on Monday, November 24. Hide Caption 4 of 34 Photos: Unrest in Ferguson Police take position during clashes with protesters on November 24. Hide Caption 5 of 34 Photos: Unrest in Ferguson A protester stands in front of police vehicles with his hands up on November 24. Hide Caption 6 of 34 Photos: Unrest in Ferguson Police in riot gear move past a burning vehicle on November 24. Hide Caption 7 of 34 Photos: Unrest in Ferguson A looter in Ferguson walks out of a burning Walgreens on November 24. Hide Caption 8 of 34 Photos: Unrest in Ferguson Riot police clash with protesters on November 24. Hide Caption 9 of 34 Photos: Unrest in Ferguson Firefighters work on extinguishing a Little Caesars restaurant on November 24. Hide Caption 10 of 34 Photos: Unrest in Ferguson Smoke fills the streets of Ferguson as buildings burn on November 24. Hide Caption 11 of 34 Photos: Unrest in Ferguson Police officers grab a protester on November 24. Hide Caption 12 of 34 Photos: Unrest in Ferguson A woman treats her face for possible tear gas exposure on November 24. Hide Caption 13 of 34 Photos: Unrest in Ferguson People walk away from a burning storage facility on November 24. Hide Caption 14 of 34 Photos: Unrest in Ferguson A man steps out of a vandalized store on November 24. Hide Caption 15 of 34 Photos: Unrest in Ferguson A police officer runs by a burning police car on November 24. Hide Caption 16 of 34 Photos: Unrest in Ferguson Police officers stand guard as protesters confront them on November 24. Hide Caption 17 of 34 Photos: Unrest in Ferguson Protesters block streets in St. Louis after the announcement of the grand jury's decision on November 24. Ferguson is a suburb of St. Louis. Hide Caption 18 of 34 Photos: Unrest in Ferguson Police confront protesters in Ferguson on November 24. Hide Caption 19 of 34 Photos: Unrest in Ferguson A police officer points his rifle at demonstrators on November 24. Hide Caption 20 of 34 Photos: Unrest in Ferguson Protesters run for shelter as smoke fills the streets of Ferguson on November 24. Hide Caption 21 of 34 Photos: Unrest in Ferguson The glass windows of a store are shattered on November 24. Hide Caption 22 of 34 Photos: Unrest in Ferguson A demonstrator listens to a car radio as the grand jury's decision is delivered in front of the Ferguson Police Department. Hide Caption 23 of 34 Photos: Unrest in Ferguson Lesley McSpadden, mother of Michael Brown, is escorted away from the Ferguson Police Department on November 24. Hide Caption 24 of 34 Photos: Unrest in Ferguson A group of protesters vandalizes a police vehicle in Ferguson on November 24. Hide Caption 25 of 34 Photos: Unrest in Ferguson Police officers confront protesters on November 24. Hide Caption 26 of 34 Photos: Unrest in Ferguson Demonstrators block traffic during a protest in front of the Ferguson Police Department on November 24. Hide Caption 27 of 34 Photos: Unrest in Ferguson Demonstrators gather outside the police station on November 24. Hide Caption 28 of 34 Photos: Unrest in Ferguson Protesters gather as they wait for the announcement of the grand jury decision on November 24. Hide Caption 29 of 34 Photos: Unrest in Ferguson Members of the media line up in a parking lot across from the Buzz Westfall Justice Center on November 24. Hide Caption 30 of 34 Photos: Unrest in Ferguson Residents begin to gather at the Michael Brown memorial ahead of the grand jury announcement. Hide Caption 31 of 34 Photos: Unrest in Ferguson National Guard troops arrive ahead of the grand jury announcement. Hide Caption 32 of 34 Photos: Unrest in Ferguson Members of the Missouri National Guard are escorted out of the Buzz Westfall Justice Center. Hide Caption 33 of 34 Photos: Unrest in Ferguson Demonstrators are confronted by police as they block a street before the grand jury announcement. Hide Caption 34 of 34

In its amendments, the City Council demanded the following changes in order for the decree to go into effect:

• That it contains no mandate for the payment of additional salary to police or other city employees.

• That it contains no mandate for staffing at the city's jail.

• That the deadlines set forth are extended.

• That the terms do not apply to other agencies that take over services currently provided by the city.

• That a provision for local preference in contractors and consultants is included.

• That goals for minority and women participation in consulting, oversight and third-party services are included.

• That monitoring fee caps are changed to $1 million over the first five years and no more than $250,000 in any single year.

'Just sign it'

Spirited public input preceded Tuesday night's vote.

"Black lives matter! Black lives matter!" chanted one community member.

Another suggested it was time to wrap up this chapter in the city's history.

"It's time to stop. Just go and sign the decree. You still haven`t settled the Mike Brown settlement," he said. "Get it done. Just sign it."

Justice Department found pattern of discrimination

The 102-page report issued by the Justice Department last March said some Ferguson police officers saw residents as "sources of revenue," leading to practices that federal investigators said disproportionately targeted black residents.

It also found evidence of racist jokes sent by some Ferguson police officers and court officials.

The department made 26 recommendations, including:

• Ferguson police provide training to ensure officers aren't using bias in policing.

• Officers practice community policing by getting out of cars and getting to know communities.

• Focus police stops, searches and ticketing on protecting the public, as opposed to fund-raising for the city.