A US House of Representatives committee has voted along party lines to hold Attorney General Eric Holder in contempt of Congress.
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 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.