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 he did not co-operate over Operation Fast and Furious were “untrue”.
The operation at the centre of the row saw US agents lose hundreds of illegal guns let into Mexico to trace arms dealers.
US border agent Brian Terry was killed in December 2010 in a shootout with illegal immigrants with a weapon linked to Fast and Furious.
The congressional investigation was opened after two guns retrieved at the scene were found to be among 2,000 weapons authorities were supposed to be tracking.