As part of a protracted pay dispute with train operating firms, the RMT trade union in Britain said on Thursday that railway workers had voted in favor of additional strike action in a new ballot.

The RMT General Secretary Mick Lynch said, “This sends a clear message to the employers that the huge anger among rail workers is very real and that they need to acknowledge that fact, face reality, and make improved proposals.”

Thousands of railway workers in Britain were already planning a strike on May 13 after the RMT rejected a new pay offer, the union said last week, in an escalation to a dispute that has resulted in disruptive strikes on the transport network since last summer.

The ballot result gives the RMT the mandate for six more months of strikes, but the union did not announce any fresh strike dates on Thursday.

Separately, British train drivers also announced three days of strikes in May and June last week, in their own dispute with train companies.

Railway workers are among hundreds of thousands across Britain including teachers, doctors, nurses and civil servants who are in pay disputes with their employers as inflation hovers around 40-year-highs of about 10%.

The Rail Delivery Group, which represents the train companies, did not immediately respond to a request for comment.