Washington (CNN) Bernie Sanders' campaign on Friday sued the Democratic National Committee in federal court after the party organization withheld the campaign's access to a crucial voter database.

The internal warfare exploded after the DNC cut off Sanders from the database and said the Vermont senator's presidential campaign exploited a software error to improperly access confidential voter information collected by Hillary Clinton's team.

The revelation poses a setback for Sanders, who is mounting a liberal challenge to the former secretary of state. The DNC database is a goldmine of information about voters and being blocked from it could complicate Sanders' outreach efforts. The timing is also challenging, just weeks before Clinton and Sanders are slated to compete in the Iowa caucuses.

And coming the day before a Democratic debate, the developments fueled a long-held belief in the Sanders camp and among his allies that the DNC has stacked the deck in favor of Clinton.

At a press conference in Washington on Friday, Sanders campaign manager Jeff Weaver accused the DNC of trying to sabotage the campaign.

"The DNC, in an inappropriate overreaction, has denied us access to our own data," Weaver said. "In other words, the leadership of the Democratic National Committee is actively trying to undermine our campaign."

What was accessed

Two senior Democrats familiar with the program and the investigation told CNN that the Sanders campaign accessed turnout projections for Iowa caucuses and the New Hampshire primary, a key piece of strategy the Clinton campaign has been working on with modeling and analytics.

The Sanders team, which consisted of four people, ran multiple searches in Iowa, New Hampshire, Nevada, South Carolina and about 10 March states, including Florida and Colorado. In Iowa and New Hampshire, the Clinton campaign has ranked voters on a scale of 1-100 for turnout, enthusiasm and support, the senior Democrats said. The Sanders campaign ran two searches: "Show me all the Clinton people rated higher than 60" and "Show me all the people rated less than 30." This would be a key way of knowing who Sanders should target in the final weeks before voting: Ignore those above 60, while focus on those below 30, because they are looking for a Clinton alternative and might be open to Sanders.

The investigation into what information was lifted should only take a few days as there are audit logs and trails of the activity, which took place beginning around 10:40 a.m. and lasting for about 40 minutes, the senior Democrats said.

They added that the Clinton campaign views this as a big deal but will not say so publicly because it will fan the flames of liberal groups trying to fight with the DNC.

In a statement released Friday afternoon, the Clinton campaign called for the Sanders campaign and the DNC to "work expeditiously to ensure that our data is not in the Sanders campaign's account and that the Sanders campaign only have access to their own data."

'Inappropriate overreaction'

At Friday's press conference, Weaver said, "The DNC is clearly acting in a heavy-handed way, in an unprecendented way. I would like to see another instance where a presidential campaign had their data -- their own data -- withheld under similar circumstances."

The Sanders campaign sought an injunction against the DNC Friday afternoon, claiming irreparable harm and seeking immediate access to the voter file system. A campaign aide said earlier Friday that there was no expectation the DNC would grant access before the close of business Friday.

Weaver said the original problem with the database's security, which did not involve the current database access company NGP VAN, dated back to October.

"We were very concerned that large amounts of our own data was being downloaded and we contacted the DNC to remedy the situation," he said. "We talked to them and we were assured that this was going to be taken care of. But apparently they are not competent in terms of maintaining the security of their data between the campaigns."

The DNC, however, had a very different story.

Shortly after Weaver's press conference, DNC chairwoman Debbie Wasserman Schultz said suspending the Sanders' campaign's access was the only way to ensure the voter file was properly safeguarded.

'Protect' voter file

"That is the only way that we can make sure that we can protect our significant asset that is the voter file and its integrity," Wasserman Schultz said on CNN.

She said "multiple staffers" from the Sanders campaign downloaded information that they did not have the right to collect.

"They not only viewed it, but they exported it and they downloaded it," Wasserman Schultz told CNN's Wolf Blitzer. "We don't know the depth of what they actually viewed and downloaded. We have to make sure that they did not manipulate the information."

She added, "That is just like if you walked into someone's home when the door was unlocked and took things that don't belong to you in order to use them for your own benefit. That's inappropriate. Unacceptable."

The DNC also sent out a strongly worded message from Wasserman Schultz to its members accusing the Sanders campaign of improper conduct.

"Over the course of approximately 45 minutes, staffers of the Bernie Sanders campaign inappropriately accessed voter targeting data belonging to the Hillary Clinton campaign," Wasserman Schultz said in the message.

"Once the DNC became aware that the Sanders campaign had inappropriately and systematically accessed Clinton campaign data, and in doing so violated the agreement that all the presidential campaigns have signed with the DNC, as the agreement provides, we directed NGP VAN [the vendor that supplies access to the database] to suspend the Sanders campaign's access to the system until the DNC is provided with a full accounting of whether or not this information was used and the way in which it was disposed," she added.

Fired Sanders staffer

Josh Uretsky, Sanders' national data director who was fired Thursday by the campaign for accessing the database, told CNN Friday that he was not trying to look at Clinton's data and denied that voter file information had been downloaded.

"We knew there was a security breach in the data, and we were just trying to understand it and what was happening," Uretsky said.

He said that none of the data the Sanders campaign accessed on Wednesday "left the system that day" and denied that he or his staff "downloaded any individual level voter file data."

Uretsky said he and his team downloaded only phone numbers but did so to alert the DNC and NGP VAN that the Sanders campaign was aware the campaigns' voter info in the DNC database wasn't being properly protected.

"We knew that what we were doing was being recorded," he told CNN. "We didn't try to be sneaky at all. They can argue that we shouldn't have done it but we did not in any way try to deceive them. We created the records of it having been done and we did not make any attempt to use it for strategic purposes."

Ethan Roeder, Barack Obama's data director in 2008 and 2012, said the biggest problem created by being barred from the database is the fact that Sanders' volunteers will not be able to use the voter file to make calls and knock on doors for at least the next few days.

"I think the pain is compounded each additional day that they don't have access to the file," Roeder said. "It definitely has an impact on their operations. Especially as close as we are to caucuses and primaries, it becomes a serious problem."

NGP VAN, the database vendor, issued a statement Friday saying the DNC had instructed the company to remove the Sanders campaign's access to the database.

"We are confident at this point that no campaigns have access to or have retained any voter file data of any other clients; with one possible exception, one of the presidential campaigns," the company said, adding that it was investigating the breach and would report back to the DNC.

Sanders supporters react

Sanders supporters and liberal groups have reacted to the news of Sanders' campaign being punished by questioning the neutrality of the DNC, hinting that the body is in the tank for Clinton.

"The Democratic National Committee's decision to attack the campaign that figured out the problem, rather than go after the vendor that made the mistake, is profoundly damaging to the party's Democratic process," said Charles Chamberlain, executive director of Democracy for America, a liberal group that endorsed Sanders this week.

"DNC leaders should immediately reverse this disturbing decision before the committee does even more to bring its neutrality in the race for President into question," he added.

Weaver, the Sanders campaign manager, said of the DNC, "In this case, it looks like they are trying to help the Clinton campaign."

"We are taking on the establishment and I'm sure there are people within the Democratic establishment who are not happy about the overwhelming success that Bernie Sanders is having all across this country," he added. "But we are determined to win this campaign and we're going to win this campaign by talking about the issues that are important to the American people. To do that we are going to need our data, which has been stolen by the DNC."