The National Rifle Association has picked up another outside lobbying firm just as the U.S. Senate prepares to hold a vote on gun control legislation as early as this week.

Greenberg Traurig is advocating for the NRA’s Institute for Legislative Action on firearms and gun control legislation, according to lobbying registration paperwork the firm filed with Congress on Monday. Michael Williams, a senior director at the firm, is handling the account. He joined Greenberg Traurig in 2001 after more than 11 years as an in-house lobbyist at the NRA.

Williams declined to elaborate on his new lobbying work for the NRA, saying the registration filing "speaks for itself."

With the addition of Greenberg Traurig, the NRA now has six firms registered to lobby for it, according to congressional records. The gun rights group spent $2.5 million on federal lobbying last year by its own staffers, as well as lobbyists from Dentons, C2 Group, Crossroads Strategies, Prime Policy Group and Shockey Scofield Solutions.

The NRA said last week it doesn’t support a gun-control measure from senators Joe Manchin III (D-W.Va.) and Patrick Toomey (R-Pa.), who are pushing for expanded criminal background checks for firearms purchases. A Senate vote on their proposal could happen this week.

"We need a serious and meaningful solution that addresses crime in cities like Chicago, addresses mental health deficiencies, while at the same time protecting the rights of those of us who are not a danger to anyone," the NRA said in a written statement.

Last week, U.S. Attorney General Eric Holder Jr., speaking at a gun safety event at the White House, urged the Senate to give its consideration to proposals the Obama administration contend will reduce gun violence.

"Let me say it more clearly than that: each of these measures deserves a vote," Holder said in prepared remarks. "The American people deserve these votes in spite of the pressure that the special interests and lobbyists are exerting in back rooms on our elected representatives."