Even as the campaign admitted its staffers had inappropriately reviewed and saved Hillary Clinton campaign data made available as a result of a software error, it emphatically accused the DNC of sabotage and of blatantly favoring Clinton.

“The leadership of the Democratic National Committee is now actively attempting to undermine our campaign. This is unacceptable,” Sanders’ campaign manager Jeff Weaver said on the eve of the third Democratic debate. “Individual leaders of the DNC can support Hillary Clinton in any way they want, but they are not going to sabotage our campaign — one of the strongest grassroots campaigns in modern history.”

The suit argues that the party is denying the campaign access to its voter data in violation of a contract governing the use of the information. The campaign contends this freeze is an illegal overreaction to the episode.

“The suspension or termination of the Campaign’s access was undertaken without contractual cause, and in contravention of the Agreement’s termination protocols,” the suit says.

“The DNC may not suspend the Campaign’s access to critical Voter Data out of haste or desperation to clean up after the DNC’s own mistakes,” the complaint adds.

At issue is a revelation that Sanders’ digital director Josh Uretsky — likely along with other staffers — took advantage of a software error this week by political data technology company NGP VAN that allowed them to see the voter file that contains vital information used by campaigns to identify and monitor voters and potential supporters.

The DNC’s punishment is a potentially crippling blow to the Vermont senator’s campaign: it means he temporarily loses access to critical voter data just weeks before voting is set to begin in Iowa and New Hampshire, where he is within striking distance of Clinton. Without access to the voter file, on-the-ground organizing will become far more difficult for Sanders.

The dispute, which broke open after Sanders had a strong day of scoring two major endorsements, set off a broader war within the Democratic Party, which has not yet fully coalesced behind Clinton. The former secretary of state is leading Sanders by more than 20 points in national polls, but Sanders has tapped into the populist urgings of the party and has a strong grassroots fundraising base.

The controversy also blew open a long-simmering dispute between the DNC and Clinton’s rival campaigns, who have long harbored resentments over the appearance that the organization was acting to boost the Democratic front-runner’s political fortunes.

DNC Chair Debbie Wasserman Schutz, speaking on CNN, said its action to suspend Sanders’ access to the voter file was “certainly not unreasonable.”

She said if the shoe was on the other foot, and the Clinton camp had accessed Sanders’ data, “I’m confident that this is the decision that they would expect from us.”

She said she had called for an independent audit and that, “We have to make sure they can’t manipulate that information until we know exactly what happened, what they have and that we can verify to each campaign that we have handled this in a way that is compliant with the agreement that they each signed.»

Weaver, however, said the retribution was unfair. He described the campaign’s data as «stolen by the DNC» and said he saw a «pattern» of actions suggesting the committee has been helping Clinton. He said he planned to bring the issue to federal court this afternoon if the DNC continues to «hold our data hostage.»

Weaver reiterated that the campaign had fired the staffer who was in charge of the breach, Uretsky, and added that the campaign was in the process of talking to other aides who were involved and that further disciplinary action may be merited.

He also acknowledged the staffers’ actions were inappropriate. «Clearly, while that information was made available to our campaign because of the incompetence of the vendor, it should not have been looked at. Period,» he said.

He also said the campaign was confident that months ago, «some of our data was lost to one of the other campaigns.»

A pair of high-profile liberal groups — MoveOn.org and Democracy For America — came to Sanders’ defense on Friday, calling on the DNC to reverse its decision. The Sanders camp handed out copies of their statements to reporters at the press conference.

But others say that the Sanders’ campaign is downplaying the extent of the inappropriate behavior.

Audit logs show that during a 40-minute span that began at 10:40 a.m., four Sanders staffers sifted through the Clinton campaign’s data and conducted 25 specialized searches, according to a person familiar with the breach. The most valuable information obtained, the source said, were lists of individuals the Clinton campaign has identified as its most hardcore supporters across 10 states, as well as lists of those individuals whose support for Clinton is wavering, and could therefore be convinced to support Sanders instead.

The lists are obtained through the time-consuming process of phone banking and, based on those conversations, scoring voters based on how likely or unlikely they are to support Clinton. Sanders camp could benefit from the lists, for instance, by saving time on hitting up those voters who are clearly for Clinton and focusing on winning over those whose support is weaker. The source estimated that the data was worth millions of dollars of investment by the Clinton campaign.

According to a review of the audit logs, Sanders operatives conducted searches for Clinton supporters over 70 — a number that indicates those voters are hard core Clinton supporters unlikely to be swayed by any outreach by the Sanders campaign. And they searched for Clinton supporters under 30, a number that showed the support was not strong and those voters could be easily swayed. The audit logs also show Sanders’ deputy national data director Russell Drapkin granting access to their colleagues to view the proprietary information.

After a day of staying mostly silent, the Clinton campaign started firing back on Friday evening. «If you are so proud of your grassroots organization, you should not need to resort to stealing campaign data,» tweeted press secretary Brian Fallon. «There is a word for this in Brooklyn: chutzpah.»

Fallon also added in a statement on Friday afternoon, “We were informed that our proprietary data was breached by Sanders campaign staff in 25 searches by four different accounts and that this data was saved into the Sanders’ campaign account. We are asking that the Sanders campaign and the DNC 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.”

The Sanders campaign is represented in the case by attorneys Benjamin Lambiotte and Sean Griffin of the Washington law firm Garvey Schubert Barer, and the case was assigned to Judge Tanya Chutkan, an Obama appointee who took the bench just last year.

Uretsky, the staffer who was fired by the Sanders campaign, appeared on MSNBC Friday afternoon to defend his actions, saying they were trying to understand the extent of the software problem.

“We could see that there was a problem in security and so we wanted to create a record on their system without taking any data for our purposes.”

When pressed about his intent, Uretsky said they assumed the Clinton campaign also had access to the overall voter database, and that they weren’t trying to hide their actions.

“The analogy would be somebody leaves the front door open … and you left a note inside the front door saying you left the door open,» he said. «And then maybe you went and checked the side door, too, to make sure that door was closed.”

Josh Gerstein, Kyle Cheney, Nick Gass and Eliza Collins contributed to this report.