In an unusual arrangement, a senior official of the Bureau of Alcohol, Tobacco, Firearms and Explosives involved in the controversial gun operation Fast and Furious is receiving his government salary while working full time for the investment bank J.P. Morgan, according to two Republican lawmakers.

In a letter Tuesday to B. Todd Jones, the acting ATF director, Rep. Darrell Issa (R-Calif.) and Sen. Charles E. Grassley (R-Iowa) said that Deputy Assistant ATF Director William McMahon, who oversaw the agency’s Western region during the Fast and Furious operation, has been receiving two salaries simultaneously.

The lawmakers said the ATF apparently approved allowing McMahon to remain on paid leave for four or five months while working for the investment bank in order to reach retirement eligibility.

“ATF has essentially facilitated McMahon’s early retirement and ability to double dip for nearly half a year by receiving two full-time paychecks — one from the taxpayer and one from the private sector,” Issa and Grassley wrote.

ATF spokesman Mike Campbell said the agency is reviewing the letter. “Due to privacy act considerations, all we can confirm is that Bill McMahon is still currently employed by ATF,” Campbell said.

The letter was provided to The Washington Post late in the day Tuesday and attempts to reach McMahon and the investment bank were unsuccessful.

McMahon is receiving a six-figure salary as an official in the ATF Office of Professional Responsibility and is serving as executive director of global security and investigations for J.P. Morgan in the Philippines, according to Issa and Grassley.

McMahon was one of five ATF officials recently singled out in a congressional report on the botched gun operation. The report alleged that McMahon knew that no safeguards were in place to prevent a large number of guns from getting into Mexico, but he made no effort to stop them.

In July, 2011, McMahon testified before the House Committee on Oversight and Government Reform and apologized for the controversial operation.

“However good our intentions, regardless of our resource challenges, and notwithstanding the difficult legal hurdles we face in fighting firearms traffickers, we made mistakes,” McMahon told the committee. “And for that I apologize.”

During the two-year operation, ATF agents watched as hundreds of weapons were purchased by gun-trafficking suspects. Some agents testified that they were ordered to let the guns “walk” so that the agency could trace the weapons to a firearms-trafficking ring. Several supervisors have said that they never allowed gun-walking but were told by the U.S. attorney’s office in Phoenix that they did not have enough evidence to seize the guns.

The Justice Department’s inspector general is expected to release a report on the operation in the coming weeks, according to law enforcement officials.