Congress is poised to kill the legal justification for President Obama's Clean Power Plan by eliminating an obscure passage in Clean Air Act amendments passed in the early 1990s.

Three top House Republicans say in a letter sent to the Environmental Protection Agency on Monday that Congress' nonpartisan Office of Law Revision Counsel ruled in 1992 that an amendment in section 111(d) of the Clean Air Act, which the agency is using to justify its power plant rules, is unenforceable. If the law is enacted as written by the office, it would replace the current Clean Air Act as law and the Clean Power Plan's legal justification would be significantly undermined.

The lawmakers also charge that the EPA may have inhibited the congressional agency from moving faster to make sure the Clean Power Plan had a legal basis.

The Clean Air Act amendments have yet to be enacted by Congress' Office of Law Revision Counsel. After laws are passed and signed, the office writes a final, clean version to publish in the U.S. Code as the final law. Bills that put laws into the U.S. Code typically pass both chambers with unanimous consent. The process started in 2009, when Democrats were in control of Congress.

House Energy and Commerce Committee Chairman Fred Upton of Michigan and Reps. Tim Murphy of Pennsylvania and Rep. Ed Whitfield of Kentucky sent a letter to EPA Administrator Gina McCarthy Monday raising questions about the agency's participation in the enactment of Clean Air Act.

The Republicans say there are serious questions about whether the EPA "worked to inhibit" the Office of Law Revision Counsel during the enactment process. Letters between the Law Revision Counsel and the EPA show the agency worried that the final version of section 111(d), which is used as the legal basis for the Clean Power Plan's emissions goals for states, would strip the agency of the legal authority to issue the plan. Section 111(d) would remain under the final rule, but an amendment in that section that the EPA uses to justify the Clean Power Plan would be removed.

"From this correspondence it appears that the agency may have been inhibiting a statutorily prescribed process because it would undermine the agency's legal arguments supporting its 111(d) rulemaking," the letter says. "EPA's failure to cooperate in this statutorily prescribed process raises serious questions about EPA's statements of authority to promulgate its 111(d) rule."

The EPA did not immediately respond to a request for comment.

The agency wrote in a July letter to the House Energy and Science Committee's regulatory reform subcommittee that if the process were completed, section 111(d) no longer would give the agency the "statutory authority to issue the Clean Power Plan and regulate greenhouse gas emissions from power plants and other stationary sources."

The current version of the law is legally admissible in court, but if the enactment process were completed, the U.S. Code would be legally stronger. The Clean Power Plan is under legal siege as 26 states have filed suit to stop the regulation, along with a number of interest groups.

The process for the law to be put in the U.S. Code could be finished in months. The House Judiciary Committee sent the final version of the Clean Air Act to the full House Oct. 27. Bills that put laws into the U.S. Code typically pass both chambers with unanimous consent.

The enactment process is meant to essentially clean up laws passed by Congress without changing their meaning, intent or effect and can take years due to the amount of required feedback. After the process is completed, the cleaned-up bill is submitted to the Judiciary Committee, where it is reviewed and then sent to the full House and Senate for votes.

Until Congress approves the new, cleaned-up bill, the obscure amendment would give the agency the legal justification it needs.

The lawmakers say the EPA might have purposely delayed the enactment process to make sure the Clean Power Plan had a legitimate legal justification.

"There is reason to believe that agency officials may have worked to inhibit the congressional Office of Law Revision Counsel as it sought to fulfill its responsibility to codify the language of the Clean Air Act and other statutory provisions," the letter states.

In its July letter, the EPA argued the enactment of the Clean Air Act amendments could complicate interpretation of the law. It accused the writers of the final bill of "selectively" using some language enacted by Congress but excluding other passages that would give it the legal authority to institute the Clean Power Plan.

The EPA declined to discuss the law with the judiciary committee in 2013, despite being given a copy of every change being made to the Clean Air Act, according to a letter sent from the Office of Law Revision Counsel to the EPA in September.

The lawmakers in their Monday letter are asking for documents and responses to multiple questions, including which EPA offices should have responded to the Law Revision Counsel, a description of all activity by EPA employees relating to the codification process and all documents the EPA possesses about the process.

The representatives also asked for all documents the EPA has showing communications between the EPA and other federal agencies, or third parties, about the enactment of the Clean Air Act.