Updated: 11:50 a.m.

A giant cross-country oil pipeline is not the only Republican-backed provision in the House tax bill that has environmentalists fired up.

Lobbyists for coal plants, electric power companies and industrial boilers are also hoping to take advantage of the last-minute legislative crunch to win rollbacks of Environmental Protection Agency emission regulations in what environmentalists describe as an eleventh-hour attempt to gut the Clean Air Act.

Advocates for the boiler industry are cheering on House Republicans as they prepare to vote on a tax package including a rider that would repeal boiler emission standards, in addition to a provision that would require the White House to approve the Keystone XL pipeline that would bring oil to the U.S. from Canadian tar sands. The bill is the Republican proposal for extending payroll tax relief into next year, a Democratic priority.

Senate Democratic leaders have said those provisions will be rejected in their chamber, and John Walke, clean air director at the Natural Resources Defense Council, said this morning that he was “guardedly optimistic” that the regulation rollbacks would not make it into the final bill. Still, energy industry experts said the boiler rule has the best chance of all the anti-EPA provisions thanks to the support of moderate Members such as Sens. Olympia Snowe (R-Maine) and Ron Wyden (D-Ore.).

The rule ­— known as the boiler maximum achievable control technology rule — governs emissions of mercury, carbon monoxide and other hazardous pollutants released by industrial and commercial boilers.

The coal industry, piggy-backing on the anti-EPA energy, is making a last-ditch effort to delay new standards on mercury emissions from coal-fired power plants. The EPA is expected to release the final language of that regulation, called the “utility MACT,” as soon as Friday, and industry groups are warning that the rule could lead to power shortages and price increases while facilities scurry to retrofit equipment in time for the 2015 compliance deadline.

The American Coalition for Clean Coal Electricity ran an open letter to the president in Capitol Hill papers Monday as part of a yearlong, $35 million effort to convince the administration to extend the compliance date by as much as two years.

The rule orders coal-fired utilities to significantly decrease the amount of mercury emitted when coal is burned. The scrubbers needed to do the job would also limit other air toxins that supporters note can cause asthma attacks, heart attacks, strokes and premature death.

A group of Republican lawmakers urged the agency to delay the coal rule in a letter to the administration today, citing “a variety of scientific and procedural issues with the agency’s pursuit of unmanageable and costly Utility MACT requirements.”

The letter, signed by Science, Space and Technology Chairman Ralph Hall (Texas), Subcommittee on Investigations and Oversight Chairman Paul Broun (Ga.) and Subcommittee on Energey and Environment Chairman Andy Harris (Md.), noted the federal court decision to temporarily block an agency rule governing cement plants’ storage of an ingredient used to make concrete, one of several emissions rules included in the “Cement MACT.”

The proposed standards for boilers and coal plants were both on a list of 10 “job destroying” regulations that House Majority Leader Eric Cantor (R-Va.) issued in late August. Since then, he’s won at least two victories: In September the Obama administration announced it would halt a plan to tighten ozone restrictions nationwide, and last week House Republicans passed legislation that would prevent the administration from cracking down on farm dust — something the EPA has said it has no intention of doing.

“Cantor’s list helped focus attention on the fact that all these rules together have a pretty severe impact on jobs,” said Paul Bailey, senior vice president for federal affairs and policy at the coal coalition. “Of course, one could argue that having the regulations on a Republican hit list may not have helped” gain Democratic support.

Roll Call reported in September on the cement industry’s concern about similar regulations, which also appeared on the list.

Bailey said if industry groups do not win the delays this time around they will work to make the coal rule and other controversial EPA regulations a political problem for Democrats in 2012.

“This is the first time that EPA regulations could have a real impact on senatorial elections,” he said. “I have no doubt that there are a lot of Members of Congress — not just Republicans — [who] have a strong, sincere feeling that EPA is out of control right now.”