Striking workers at Metro’s Cinder Bed Road bus garage in Lorton will return to work while their union continues negotiations with Transdev, the private contractor that employs them, according to an agreement outlined in a letter obtained Monday by The Washington Post. But a union leader called the description of the deal “misleading.”

The agreement is the outgrowth of a four-year deal that Metro reached last week with its largest union, Amalgamated Transit Union Local 689.

In the letter sent Monday to John King, regional vice president for Transdev North America, Metro General Manager Paul J. Weidefeld wrote that once the contract is approved by ATU’s members and by Metro’s board of directors, the Cinder Bed Road workers will return to their jobs.

“As a result of this agreement, the ATU has agreed to return employees to duty status at the Cinder Bed Road facility while Transdev continues to negotiate with the ATU,” Weidefeld wrote. According to the letter, ratification of the labor agreement is expected “within the week.”

Metro officials declined to comment.

In a statement, Brian Wivell, a political organizer for ATU Local 689, said, “This union only agreed that employees could return to work if and when Transdev provides assurances that no workers will be harassed or retaliated against for exercising their right to strike.”

“We also want assurances that Transdev will actually bargain in good faith,” Wivell said. “We are also fully willing to walk back out if Transdev continues to waste time, stall, and delay at the bargaining table with insulting offers.”

Mitun Seguin, a spokeswoman for Transdev, said that company executives were in transit and could not be reached for comment but that the company and ATU “have been in conversations to bring the drivers back.”

The nearly 120 Metrobus operators and garage workers at the Cinder Bed Road facility have been on strike since Oct. 24, part of a dispute with Transdev, a France-based multinational transit corporation with whom Metro contracts to run the operations.

Workers at the garage have demanded wages and benefits similar to those of workers employed by Metro. ATU officials said starting pay for Metrobus drivers and those employed by Transdev is about the same, but those who work for Metro can eventually earn up to $34 an hour. The union says workers employed by Transdev have not received a raise since the garage opened about two years ago, and have no provision in their contract for scheduled raises. Their health benefits also have a $6,000 deductible.

In his letter, Weidefeld also warned Transdev against taking any action against workers once they return to their jobs.

“As Transdev employees return to active duty status at the Cinder Bed Road facility, I am seeking assurances from you that all employees will be treated fairly without prejudice or retaliation and welcomed back to Transdev,” Weidefeld wrote. “Transdev is responsible for ensuring a safe working environment at the facility for its employees, contractors, subcontractors, and visitors. We also expect Transdev to immediately and fully restore all services required by our Contract.”

The Cinder Bed Road garage is the base for 18 Metrobus routes that crisscross mainly Northern Virginia and serve about 8,500 commuters each weekday.

The facility is the only portion of Metro’s main transit services that has been fully privatized. Metro chose Transdev to operate the facility two years ago and awarded it a three-year, $89 million contract with two one-year options. Metro officials viewed the deal as a way to save $15 million over five years by not paying the new garage employees Metro pensions and retirement benefits. But as part of the four-year agreement it reached with the union last week, the transit agency will not seek to outsource additional operations and will scrap a plan to privatize operations on Phase 2 of the Silver Line.

Transdev also was at the center of another strike. On Dec. 5, nearly 600 Fairfax Connector workers walked off the job, leaving an estimated 30,000 Northern Virginia bus riders without service. However, those workers agreed to return to work Dec. 9 while talks continued. The Fairfax Connector workers also are represented by the ATU.

Justin George contributed to this report.