A US House of Representatives committee has voted along party lines to hold Attorney General Eric Holder in contempt of Congress.
This comes after Holder refused to hand over papers relating to a botched sting operation.
However, Holder said claims that he did not co-operate with the probe into the sting operation dubbed Fast and Furious are not true.
US President Barack Obama has used his executive privilege to withhold documents being sought by the House Oversight Committee.
The operation at the centre of the controversy 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 during a shootout with illegal immigrants with a weapon that was linked to Operation Fast and Furious.
The congressional investigation began after two guns retrieved at the scene were found to be among 2,000 weapons, which authorities were supposed to have been tracking.