Members and supporters of the United Mine Workers of America demonstrate outside BlackRock headquarters on Nov. 4 in New York. Mary Altaffer/Associated Press, file

BIRMINGHAM, Ala. — A federal oversight board ordered the United Mine Workers of America to pay more than $13 million in compensation to an Alabama coal company where members have been on strike for more than a year, a ruling the union said Wednesday it would challenge.

The National Labor Relations Board said Warrior Met Coal Mining was due some $13.3 million for costs including increased security, damage repair and lost revenues from unmined coal, and individuals were due almost $30,000, mostly for damage to vehicles. Both amounts included interest.

The union, with roughly 1,100 members who went on strike against the Alabama-based company on April 1, 2021, called the NLRB assessment an “outrageous” decision that it planned to fight.

“Is it now the policy of the federal government that unions be required to pay a company’s losses as a consequence of their members exercising their rights as working people? This is outrageous and effectively negates workers’ right to strike. It cannot stand,” international union president Cecil E. Roberts said in a statement.

A company representative did not immediately return an email seeking comment. The NLRB, which is handling charges related to both the company and the union, issued the order on July 22.

The union and company signed an agreement providing that the union pay damages for “strike misconduct,” and the board approved it, spokeswoman Kayla Blado said. The agency is currently assessing the cost, she said.

“If there is not agreement with the region’s ultimate conclusion, the region will commence a proceeding before an administrative law judge where the parties can present arguments and evidence about what each considers to be appropriate damages,” she said in a statement.

Both the union and Warrior Met have blamed each other for the prolonged strike, which centers on the company’s mining operations southwest of Birmingham. The two sides have talked as recently as last week, a union spokesman said.

The union is striking at Warrior Met’s No. 4 and No. 7 mines, a preparation plant and a central shop, all in Tuscaloosa County. The union and Warrior Met reached an agreement to end the walkout a few days after it began, but members rebuffed the settlement.

United Mine Workers has said union members gave up money to bring the company out of the Walter Energy bankruptcy six years ago, and workers have sought improved health benefits. Warrior Met contends it offered workers a competitive package that would protect jobs and the company’s future.

In May, Warrior Met reported net income of $146.2 million in the first quarter compared with a loss of $21.4 million for the same period last year. The company said the strike cost it $6.7 million for the quarter because of security and other expenses, and having the mines idle cost $3 million.

Warrior Met said it produced 1.5 million short tons of coal in the first quarter compared with 2.2 million short tons in the first quarter last year.