A US House of Representatives committee has voted along party lines to hold Attorney General Eric Holder in contempt of Congress.
Mr Holder refused to hand over papers relating to a botched sting operation.
The move comes after President Barack Obama used his executive privilege to withhold documents sought by the House Oversight Committee.
But Mr Holder said claims that he did not co-operate over Operation Fast and Furious were "untrue".
In December 2010, US border agent Brian Terry was killed in a shootout with illegal immigrants with a weapon linked to Fast and Furious.
In the congressional investigation which followed, two guns recovered from the scene were found to be among 2,000 weapons the authorities were supposed to be tracking, as part of an operation to tackle cross-border gun trafficking.
Republican leaders in the House of Representatives have said they will schedule a full vote next week on the issue.
Shortly after the committee vote, House Speaker John Boehner tweeted an ultimatum, saying a full House vote would be held unless Mr Holder co-operated with the inquiry.
Mr Holder's reaction was swift and combative.
Committee chairman Representative Darrell Issa has "chosen to use his authority to take an extraordinary, unprecedented and entirely unnecessary action, intended to provoke an avoidable conflict between Congress and the Executive Branch," Mr Holder said.
"This divisive action does not help us fix the problems that led to this operation or previous ones and it does nothing to make any of our law enforcement agents safer," he said, calling it "an election-year tactic".
The Department of Justice says it has denied access to the files because they contain information that could affect criminal investigations.
Its officials say they have already sent more than 7,000 documents to the Republican-led House Oversight Committee.
Wednesday's use of executive privilege for withholding documents is the first time Mr Obama has invoked the power. Former Presidents George W Bush and Bill Clinton used the privilege six and 14 times respectively during their eight-year terms.
On Tuesday, Mr Holder met Mr Issa, but they did not agree on a path forward.
Mr Holder said lawmakers had turned down his offer to give them the documents, along with a briefing on the operation, in exchange for assurances that the panel would drop contempt proceedings.
Officials charged with contempt of Congress could potentially be fined or jailed - but correspondents say this standoff is unlikely to provoke such an outcome.
Historically, Congress and the White House have negotiated agreements to avoid a court battle that would limit either Congress' subpoena power or executive privilege itself.
In a separate development on Tuesday, the family of an Immigration and Customs Enforcement agent killed in Mexico has filed a $25m wrongful death lawsuit against several US officials, including Mr Holder.
Jaime Zapata's family say the weapons that killed him were brought into Mexico because of US investigations into gun trafficking.