In a 50-49 vote, the Senate quashed Labor Department rules from the Obama administration that would have made it easier for cities to provide government-run retirement plans to private sector workers.
Trade groups from the financial services industry applauded the measure while consumer advocates worried that it will be harder to help the roughly 55 million employees who don't have access to a workplace retirement plan.
Several municipal governments, including New York, Philadelphia and Seattle, have considered creating city-run retirement plans for people without workplace options.
"The regulation puts private marketplace plans at a disadvantage. This vote wisely overturns the regulation," Dirk Kempthorne, president and CEO of the American Council of Life Insurers, said in a statement.
The House has passed a similar bill and another one that would make it more difficult for states to provide retirement plans to private sector workers. The Senate has yet to vote on a bill that would affect state-run plans.
Lawmakers in 30 states have considered providing government-run retirement plans to private sector workers.
The Senate vote on repealing rules for state-run plans may face stronger opposition.
Seven states already have approved programs: California, Connecticut, Illinois, Maryland, New Jersey, Oregon and Washington state. Oregon is scheduled to open its retirement plan to a small group of workers starting July 1.
"It was a razor-thin vote and we hope we can educate a few more senators to defeat the bill [that would affect state-run retirement plans]," said Karen Friedman, the Pension Rights Center's executive vice president and policy director.