One of the unions at Tata Steel’s plants in south Wales has announced it will begin industrial action on 18 June.

Unite said members at Port Talbot and Llanwern would begin a “work to rule” and overtime ban in protest at the company’s plans to close both blast furnaces with the loss of 2,800 jobs across its UK operations.

Tata Steel UK, which is proposing to build a greener electric arc furnace at the Port Talbot site, said it was disappointed, but that the current business was “unsustainable”, losing £364m in 2023-24.

The Community union, which represents the bulk of workers at Port Talbot, has told its members that it is considering an improved redundancy offer which it will put to them once negotiations are completed.

All three of the unions at Tata’s Port Talbot site, the UK’s biggest steel plant, have balloted for industrial action, but Unite is the only one to announce dates.

Tata has previously warned that it could withdraw the enhanced redundancy packages on offer if workers take industrial action.

Peter Hughes, Unite’s regional secretary for Wales, said: “Our members will not stand quietly by and allow Tata to needlessly trash jobs and communities and commit serious harm to both the Welsh economy and national security.”

The union said that “strike action will be scheduled if the company does not row back on its plans.”

Last week the Community union, which also opposes Tata’s plans, wrote to its members telling them the company had further improved its redundancy support package.

The letter said Community was continuing wider negotiations to “get the best deal possible for all workers affected, as well as the best deal possible to ensure future investment for Port Talbot and the downstream sites”.

It said those changes would be put to members “to have their say” once the negotiations were finalised.

Tata recently announced that it had agreed a deal with the National Grid to supply electricity for the new electric arc furnace in 2027.

The UK government is providing a £500m subsidy to support the building of the electric arc furnace which will cost a total of £1.25 billion.

Responding to Unite’s announcement of industrial action, Tata said it had repeatedly written to Unite raising concerns about “significant irregularities in the ballot process” for industrial action.

The company also said that by restructuring its UK operations “we will be able to sustain the business as we transition to new electric arc furnace technology.”

A transition board has been set up, with a £100m fund to support workers who face losing their jobs.