WASHINGTON — Senate Republicans are trying an unusual tactic to nullify new labor regulations that would speed up the time frame for unions to hold workplace elections.

The Senate will vote today on a rarely invoked measure, known as a resolution of disapproval, to overturn rules approved last year by the National Labor Relations Board.

Though the measure has little chance of passage — it also faces a White House veto threat — the vote forces Democrats in tough elections to take a stand on rules that have won praise from unions and sharp rebukes from business groups.

The rules simplify procedures and reduce legal delays that can hold up union elections after employees at a work site gather enough signatures to hold a unionization vote. They are set to take effect on April 30.

Unions call the changes a modest fix that would limit corporate stalling tactics, where litigation can delay elections while workers can be subject to harassment, threats and even illegal firing.

During debate Monday, Republicans argued the new rules would lead to “ambush” elections that barely leave company managers enough time to respond or counsel against forming a union.

“The NLRB has chosen to impose new rules to aid big labor at the expense of employees, small business employers and the jobs they would create,” said Sen. Mike Enzi of Wyoming, top Republican on the Senate Health, Education, Labor and Pensions Committee.

Sen. Tom Harkin, D-Iowa, called the vote “the latest chapter in an unprecedented Republican assault on unions.” Harkin, who chairs the Senate committee overseeing labor, said employers “have ample opportunity to express their views” on unions.

Business groups including the U.S. Chamber of Commerce and the National Association of Manufacturers have designated the vote a “key vote” — used to score members of Congress each year on their records. The AFL-CIO has also aggressively lobbied lawmakers to vote against the measure.