The Senate rejected a Republican attempt Tuesday to overturn new regulations designed to give unions quicker representation elections in their effort to organize more workplaces.

The largely party-line 54 to 45 vote against a resolution of disapproval leaves intact National Labor Relations Board rules that are scheduled to take effect Monday. Unions had sought the rule changes, while business groups opposed them. Senate Democrats unanimously supported the new regulations. Sen. Lisa Murkowski of Alaska was the only Republican to vote in support of them.

Under existing regulations, workers typically vote 45 to 60 days after a union gathers enough signatures from workers saying they want to hold an election. The new rules could cut that time by days or even weeks by simplifying procedures and putting off some challenges until after the election is held, cutting back hearings and reducing legal delays.

Unions call the changes modest fixes to prevent companies from delaying a vote while pressuring workers to reject union representation. Republicans argue that the new rules will lead to “ambush” elections that barely leave company managers enough time to respond or counsel against forming a union.

The NLRB has been the focus of intense partisan bickering since President Obama gave the independent agency its first Democratic majority in nearly a decade. The board has issued a number of rules and decisions that tend to favor unions over business interests.

“The National Labor Relations Board seems to be . . . bent on changing processes across the board more for political reasons than for substantive reasons,” Sen. Lindsey O. Graham (R-S.C.) said during floor debate.

But Democrats said the rules address some of the most abusive situations in which companies manipulate procedures to conduct anti-union campaigns.

“All the board has done is to send a clear message to employers: You can’t abuse the process to buy yourself more time to intimidate workers,” said Sen. Tom Harkin (D-Iowa), chairman of the Senate Health, Education, Labor and Pensions Committee.

The new rules could help unions expand in the private sector, where membership has dwindled to about 6.9 percent of all workers. Retailers such as Target and Wal-Mart are concerned that the new rules will encourage unions to step up organizing at their stores.

“With only about 5 percent average unionization, retailers are low-hanging fruit for union organizers,” said David French, vice president of government relations for the National Retail Federation.

The GOP measure had little chance of passing the Democratic-controlled Senate and faced a White House veto. But it forced some Democrats who face tough reelection bids to take a stand on an issue that has riled business groups.

The U.S. Chamber of Commerce and the National Association of Manufacturers designated the vote “key” — a ranking used to score members of Congress each year on their records.

Senate Republicans plan to vote on another resolution of disapproval later this year to overturn an Environmental Protection Agency rule that set the first national air pollution standards for toxic mercury from the nation’s power plants.

The tactic to nullify regulations has succeeded only once. In 2001, Congress repealed ergonomic regulations that had been approved by the Occupational Safety and Health Administration.

— Associated Press