(In April 27 story, corrects name of Republican senator who has said he will not vote for the resolution to Bob Corker instead of Tom Cotton, paragraph 11)

WASHINGTON (Reuters) - Lawmakers, lobbyists and interest groups are making a final push in their fight over regulations enacted during former President Barack Obama’s last months in office, with the financial services industry working hard to kill a rule on retirement plans run by states.

Using an obscure 1996 law known as the Congressional Review Act, Republicans have passed 13 resolutions killing Obama-era regulations on energy, the environment, gun control, education, family-planning funding and corruption. Once the rules are eliminated, agencies can never create “substantially similar” regulation.

The deadline for introducing any new CRA resolutions on regulations enacted under Obama was nearly a month ago, and Republicans are working to complete resolutions already in the legislative pipeline before the third week of May.

Currently, the resolutions only require simple majorities to pass both houses of Congress to reach President Donald Trump for signing. After May 11, they must win 60 votes in the Senate to pass, a steep hurdle, given voting margins on CRA resolutions have been tight and Vice President Mike Pence had to break a tie on one.

A spokeswoman for Speaker Paul Ryan said the House of Representatives will probably not have any more CRA votes.

A spokesman for Senate Majority Leader Mitch McConnell said McConnell “has expressed interest in considering more” resolutions.

The resolution on state-run retirement plans has been caught in limbo for weeks. Obama’s Labor Department had exempted both state and city-run retirement plans from the 1974 Employee Retirement Income Security Act, or ERISA, a law designed to protect workers’ savings with detailed compliance requirements.

Private-sector workers whose employers do not offer 401(k) or other retirement benefits, and who often have low incomes, are automatically enrolled in plans being launched in some states, such as California and Illinois. States say the exemption lets employers pass workers’ money into plans without footing compliance costs.

States are farther along than cities in establishing the programs, with cities still in the drafting stages. On March 30, the Senate approved a resolution already passed in the House killing the exemption for city programs. Trump signed it in mid-April.

Voting on a near identical resolution on states’ programs was expected to follow immediately, but so far the measure has not come to the floor.

Congressional aides say it has been hard to collect enough Republican votes to pass the measure. Republican Senator Bob Corker, of Tennessee, has stated that he will not vote for the resolution, and aides say Republican Senators Rand Paul, of Kentucky, and Todd Young, of Indiana, are also leaning to vote against it. The two senators’ offices did not respond to queries about their intentions.

Lobbyists, though, are turning up the heat.

In an April 27 letter, groups including the Investment Company Institute and U.S. Chamber of Congress wrote to all 100 U.S. senators urging them to repeal the state retirement plan rule, saying workers could be left unprotected.