“VTA recognizes that ATU employees have the right to strike so long as they comply with the law and the collective bargaining agreement,” the agency said in a statement Tuesday. “However, ATU has failed to meet those requirements prior to initiating their strike.”

Raj Singh, the president of ATU Local 265, did not immediately respond to a request for comment about the lawsuit on Tuesday afternoon.

The agency and the union began new contract negotiations in August and even went through a round of mediation at the start of this year, but the two sides are still far apart on the critical issue of wages.

VTA’s latest offer, made on Feb. 28, includes a 9% raise spread over three years, with 4% offered in the first year, then 3% and 2%, respectively, in the latter years.

On the same day, the union requested an 18% raise over the same three-year period, with 6% raises each year.

Union officials have also said they are seeking a fairer arbitration process for workers who file grievances with the VTA and other deal points, including long-term leave due to injury and illness, which the agency is seeking to cut from two years to one.

Ahead of the strike, VTA Deputy General Manager Greg Richardson characterized the union’s wage demands as “unreasonable” and said the agency can’t afford that level of pay increases without reducing services and possibly cutting jobs.

This is a developing story, and it will be updated.