WASHINGTON (Reuters) - In a last-ditch effort, five U.S. Senate Democrats are urging President Donald Trump to veto a resolution that would repeal a Labor Department rule designed to help cities launch retirement savings plans for low-income private-sector workers by exempting such programs from strict federal pension protection laws.

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In an April 5 letter that Reuters saw on Thursday, the lawmakers told Trump, a Republican, that killing the rule could harm more than 2 million Americans who would otherwise benefit from city-run retirement plans.

“We ask you to work with us to increase access to retirement savings programs and promote greater retirement security,” they wrote.

The senators signing the letter are Patty Murray of Washington and Ron Wyden of Oregon, the top Democrats on committees overseeing pensions and tax matters; Maria Cantwell of Washington; Kirsten Gillibrand of New York; and Robert Casey of Pennsylvania.

The resolution on city-run retirement plans is one of 13 measures that Congress has passed to repeal rules enacted under previous president Barack Obama, a Democrat.

An obscure law called the Congressional Review Act gives Congress a tool to repeal regulations that it finds objectionable. All that is required is a simple majority vote in both chambers and the president’s signature.

The law is limited, however, in how it can be used. Only rules that were finalized within 60 legislative days are eligible for repeal.

Trump has signed 11 of the 13 resolutions so far.

The White House Office of Management and Budget has advised Trump to sign the city-run retirement plan measure, and a White House official said on Wednesday that the president would sign more resolutions this month.

The Labor Department adopted two rules at the end of Obama’s tenure that exempted both city and state-run retirement plans from the Employee Retirement Income Security Act, or ERISA, a law designed to protect workers’ savings.

The plans are geared toward private-sector workers whose employers do not offer 401(k) or other retirement benefits, and would let them enroll automatically in plans like those being introduced in places like California.

Cities and states say they need the exemption for the plans to work effectively, but trade groups like the Chamber of Commerce and Investment Company Institute want it repealed amid concerns that workers would not have adequate pension protections.

The resolution to repeal the city-run retirement plan rule narrowly passed the Senate in a 50-49 vote.

The Senate is expected to take up a separate resolution to repeal the rule on state-run retirement plans after the Easter recess.