The Seattle City Council has unanimously approved an ordinance Monday to phase in a $15 hourly minimum wage — the highest in the nation.

Drafted by an advisory group of labor, business and nonprofit representatives convened by Mayor Ed Murray, the ordinance phases in wage increases over three to seven years, depending on the size of the business and employee benefits.

After more than four months of discussion, the group presented its plan last month. Last week the Council delayed implementation by the few months and approved a sub-minimum wage for teenagers, a provision opposed by labor representatives.

The issue has dominated politics in the liberal municipality for months. Murray, who was elected last year, had promised in his campaign to raise the minimum wage to $15 an hour. A newly elected socialist City Council member, Kshama Sawant, had pushed the idea as well.

"This legislation sends a message heard around the world: Seattle wants to stop the race to the bottom in wages and that we deplore the growth in income inequality and the widening gap between the rich and the poor," Councilmember Tom Rasmussen said.

Meanwhile, a group called 15 Now, led by Sawant, is collecting signatures for a ballot measure that would create an immediate wage hike for large businesses and a three-year phase-in for small businesses.

Chants of "we're unstoppable, we made 15 possible" erupted from supporters of the higher minimum wage after the bill was passed.

Sawant was the most vocal of the councilmembers in calling for higher wages across the board.

“Seattle is going to be the place with the highest minimum wage in the country. It is incumbent on Seattle leadership to vote for the interest of workers so we set the right precedent,” Sawant said.

But not everyone supports the increase or the different timescales on which it is being applied. Immediately following the vote, the International Franchise Association president and CEO announced a lawsuit would be filed against the “unfair and discriminatory Seattle minimum wage plan,” according to local Seattle news station KIRO-TV.

“The Seattle City Council and Mayor Murray’s plan would force the 600 franchisees in Seattle, which own 1,700 franchise locations employing 19,000 workers, to adopt the full $15 minimum wage in three years, while most other small business owners would have seven years to adopt the $15 wage,” Steve Caldeira said in a news release. “These hundreds of franchise small business owners are being punished simply because they chose to operate as franchisees.

“Decades of legal precedent have held that franchise businesses are independently owned businesses and are not operated by the brand’s corporate headquarters.”

The increase in minimum wage comes amid a national movement from low-wage workers for higher pay, and a more livable minimum wage.

Although some local businesses have come out in support of the measure, a group of restaurant owners oppose it, saying it would force them to scuttle expansion plans, decrease hiring and possibly cut service hours.

Nick Musser, executive chef and general manager of the Icon Grill in downtown Seattle, doesn't think the wage credit for tips should phase out after 7 years and finds the differentiation between large and big companies irrelevant.

"The reality is that the larger companies are going to ratchet up their wages, and we're going to have to play at that level anyway," said Musser, whose restaurant employs between 50 and 60 people, most of whom are paid minimum wage.

Ubah Aden, 40, a Seattle home health worker who says she now earns $10.95 an hour, is looking forward to the way a higher wage will help her support her three children. But she also likes the idea of Seattle setting an example for the rest of the nation.

"If this passes, then it will pave the way for other cities and states. I really think so," Aden said.

She said she and her three kids are living with her brother because she can't afford an apartment of her own even though she works full time. "This will make changes to myself and also a lot of other people in my shoes."

At the moment, San Francisco has the nation's highest hourly minimum wage at $10.74. The current minimum wage in Washington state is $9.32 an hour.

Earlier this year Minnesota raised the state's guaranteed wage by more than $3, to $9.50, by 2016. California, Connecticut and Maryland also have passed laws increasing their respective wages to $10 or more in coming years.

President Barack Obama has publicly supported increasing the minimum wage, and unilaterally increased the minimum wage of federal employees to $10.10 an hour with an executive order, effectively bypassing a stagnant Congress.

Across the country, low-wage workers have walked off the job in protest of their low pay.

More than 100 McDonald's workers were arrested after staging a sit-in and blocking the entrance to the company's headquarters in Oak Brook, Illinois on May 21, a day before the McDonald's annual shareholders meeting, according to labor activists.

Unions worldwide have joined forces to ask for better pay and working conditions at the fast-food chain, and similar actions are playing out at other similar fast food companies.

Al Jazeera and The Associated Press