A group of more than 10 conservative and free-market groups launched an eleventh-hour push in the Senate Wednesday to pressure lawmakers to pass a bill repealing an Obama-era climate change rule before next week's deadline.

The House passed a resolution months ago to repeal an Interior Department methane emission rule for the oil and natural gas industry. But the bill has languished since then in the Senate, with no likely plan for moving it to President Trump's desk.

The rules are part of former President Barack Obama's climate change agenda, but based on the Obama Environmental Protection Agency's own studies, it is completely unneeded, the groups argue.

"The rule is entirely unnecessary," read a joint letter sent by the groups to senators Wednesday. "The EPA found that methane emissions fell by 13 percent from 2011-2014. The EPA also found that methane emissions from hydraulic fracturing fell 81 percent between 2012 and 2014. This drop in methane emissions occurred even as U.S. oil and gas production has significantly increased due to the shale revolution."

The letter included the American Energy Alliance, Competitive Enterprise Institute, Americans for Tax Reform, Americans for Prosperity, American Commitment, FreedomWorks, American Council for Capital Formation, Taxpayers Protection Alliance, Coalition Opposed to Additional Spending and Taxes (COAST), Frontiers of Freedom, and Institute for Liberty.

The letter was sent to all senators, urging them to pile pressure on the GOP leadership to pass the bill before the May 11 deadline.

"The American people expect you to promote pro-growth policies that support affordable energy, jobs and economic freedom," the letter stated. "The ... methane rule is not one of those policies. ... We ask the majority leader to bring this resolution to the floor and urge all senators to vote yes."

The Congress has a limited amount of time to pass resolutions of disapproval to repeal a regulation under the Congressional Review Act.

Congress has moved similar CRA resolutions to the president's desk since January, using its authority to reverse regulations on fracking and the coal industries.

The holdup in the Senate may be due to some lawmakers believing that repealing the regulation would make it impossible to enact similar rules to reduce methane in the future, according to the letter.

"Some senators have voiced concerns that CRA method precludes future regulations. This concern is misplaced," the groups wrote. "The rule, as written, is meant to regulate methane emissions for air quality. However, [the Interior Department] only has the authority to regulate waste —the EPA regulates air quality and already has a methane regulation in place," it said.

"Regardless of your position on the regulation, it is clear that the [Interior Department's Bureau of Land Management] is far afield from its jurisdiction," the letter added.

Nevertheless, Republican senators who support ethanol fuels also may be to blame for some of the delay, according to recent reports.

A group of senators led by John Thune, R-S.D., and Charles Grassley, R-Iowa, want to trade a vote on a bill to eliminate a restriction on selling higher blends of gasoline and ethanol in the summer for a vote on the methane resolution, the Hill reported.

Thune said they tried to get it included in the government spending bill, to no avail. Not they are looking for new avenues, which has them eyeing the resolution of disapproval.

"We tried to get it included in the [spending bill], unsuccessfully. So we're looking now for other vehicles and seeing … how methane fits into that picture," Thune said Wednesday.

Other lawmakers don't believe the resolution on methane is the right venue for the ethanol change. Thune and Grassley want to end a restriction on 15-percent ethanol blends by eliminating a fuel volatility rule that restricts its use during the summer driving season.