(Reuters) - The union representing the Dartmouth College men's basketball team has filed an unfair labor practice complaint against the Ivy League school for refusing to bargain with the players, who in March became the first U.S. college athletes to unionize.

The Service Employees International Union Local 560, which represents other workers at Dartmouth, filed the complaint with the National Labor Relations Board on Tuesday. Calls to a phone number listed for the union's representative in the complaint file on the NLRB's website were not answered.

"For nearly 60 years, Dartmouth has followed a tradition of bargaining fair and equitable union contracts with our local," the college's student newspaper, the Dartmouth, quoted union President Chris Peck as saying on Wednesday. "It is past time for Dartmouth administration to avoid the looming financial and legal liabilities by grasping this opportunity to show leadership."

Members of the basketball team voted 13-2 to unionize on March 5 after NLRB Regional Director Laura Sacks ruled that the players were employees of the prestigious school in Hanover, New Hampshire. Later that month, Dartmouth declined to enter a collective bargaining agreement with the players.

"We maintain that the regional director made an extraordinary mistake," said Dartmouth in a statement. "Varsity athletes in the Ivy League are not employees; they are students whose educational program includes athletics."

College athletes have been seeking more autonomy and access to the revenue their games generate for a multibillion-dollar sports industry, which is mostly funneled to schools and their coaches.

In 2021, the National Collegiate Athletic Association allowed student athletes to sell the rights to their name, image and likeness, opening the path to sponsorship and endorsement deals.

Dartmouth has asked the NLRB for a full board review of Sacks' decision and plans to appeal the unfair labor practice charge.

"It is an unprecedented step in Dartmouth's long history of labor negotiations, but it is the only lever we can engage to ensure this matter is reviewed by a federal court," the school said.

(Reporting by Liya Cui in New York; Editing by Matthew Lewis)