The Biden administration announced on Tuesday that it had finalized a new rule that will require the nation’s largest freight railroads to maintain their current staffing of two crew members per train, settling a contentious issue between organized labor and the industry.

Federal regulations had not previously specified a minimum crew size, but the nation’s largest freight railroads typically have two workers on each train, an engineer and a conductor. The industry’s adoption of efficiency measures known as precision scheduled railroading had stoked fears among workers that freight rail companies would move to reduce their crews to one person per train as a way of further cutting costs.

The Federal Railroad Administration proposed requiring two-person crews in 2022, arguing that doing so would improve safety. The issue received further attention after a Norfolk Southern freight train derailed last year in East Palestine, Ohio, putting the issue of railroad safety in the spotlight. A bipartisan rail safety bill introduced in Congress in response to the derailment included a requirement for two-person crews, though the legislation has stalled.

The Norfolk Southern train, which investigators believe derailed because of an overheated wheel bearing, had three crew members on board: an engineer, a conductor and a conductor trainee.

“Common sense tells us that large freight trains, some of which can be over three miles long, should have at least two crew members on board — and now there’s a federal regulation in place to ensure trains are safely staffed,” Transportation Secretary Pete Buttigieg said in a statement. “This rule requiring safe train crew sizes is long overdue, and we are proud to deliver this change that will make workers, passengers and communities safer.”

In a statement, Edward A. Hall, the national president of the Brotherhood of Locomotive Engineers and Trainmen, said 11 states already required two-person crews. He called the administration’s action “an important step in making railroading safer in every state, rather than a piecemeal approach.”

The Association of American Railroads, a trade group that represents the major freight railroads, has long opposed mandating two-person crews, saying the federal government and unions have not provided evidence connecting crew size to safety.

In a statement, the group noted that in 2019, when President Donald J. Trump was in office, the Federal Railroad Administration abandoned a similar effort to require two-person crews, saying it could not justify the safety need for such a rule.

“F.R.A. is doubling down on an unfounded and unnecessary regulation that has no proven connection to rail safety,” said Ian Jefferies, the chief executive of the Association of American Railroads. “Instead of prioritizing data-backed solutions to build a safer future for rail, F.R.A. is looking to the past and upending the collective bargaining process.”