House GOP leaders cranked up the heat on Attorney General Eric Holder today, demanding he release more information regarding a failed Department of Justice program that resulted in thousands of guns being sent to Mexican drug cartels.

In a letter to Holder, Speaker John Boehner (Ohio), Majority Leader Eric Cantor (Va.) and Majority Whip Kevin McCarthy (Calif.) warn they are unhappy with the level of cooperation Oversight and Government Reform Chairman Darrell Issa (Calif.) has received in his ongoing inquiry in the “Fast and Furious” program.

“We write to express our concerns with the lack of full cooperation from the Department of Justice,” wrote the leaders, who were joined in the letter by Issa.

“As co-equal branches of the U.S. Government, the relationship between the Legislative and Executive branches must be predicated on honest communications and cannot be clouded by allegations of obstruction. If necessary, the House will act to fulfill our Constitutional obligations in the coming weeks,” Boehner and his colleagues warn.

“It is our hope that, with your cooperation, this sad chapter in the history of American law enforcement can be put behind us,” they add.

The letter is the strongest statement to date from leadership on Holder and is a clear signal their patience with the standoff between the attorney general and Issa is wearing thin.

The letter comes on the heels of a letter signed by six House GOP freshmen on the Judiciary Committee urging Boehner to bring Issa’s contempt of Congress resolution against Holder to the floor — a move he has thus far resisted.

At issue is Issa’s investigation of Operation Fast and Furious, a 2010 gun-smuggling investigation by the Bureau of Alcohol, Tobacco, Firearms and Explosives. In the operation, ATF agents allowed guns to “walk,” which meant ending surveillance on high-powered weapons suspected to be en route to Mexican drug cartels.

DOJ has resisted providing the thousands of documents Issa has demanded, in part over concerns that they could jeopardize operations currently under way.

But Boehner and his team brush aside complaints by DOJ that providing more information could cripple ongoing criminal investigations. “Whether the information used to justify the wiretap application or the information gained from the wiretaps is being used in any ongoing criminal prosecution is immaterial to the question of who on your leadership team reviewed and approved the wiretaps and was therefore privy to the details of the Fast & Furious operation.

“The assertion that your leadership team could approve wiretaps in 2010 and yet not have any knowledge of the tactics used in Fast & Furious until 2011 simply cannot be accurate and furthers the perception that the Department is not being forthright with Congress,” they added.

Meanwhile, groups sympathetic to Holder have begun pushing back against Issa’s move to bring his contempt resolution to the floor. For instance, earlier this week, the National Organization of Black Law Enforcement Executives wrote to House and Senate committees investigating Fast and Furious to “express our unwavering support of Attorney General Eric Holder and the U.S. Department of Justice (DOJ), and their commitment to enhancing state and local law enforcement,” according to a copy of the letter.

“We are concerned about reported threats to find the Attorney General in contempt of Congress in part for protecting information related to ongoing criminal investigations from political interference and public disclosure,” NOBLE added.