Workers at steel giant Tata have launched a work to rule and overtime ban in protest at the company’s plans to close blast furnaces at its biggest plant.

Tata is switching to a greener form of production at Port Talbot in south Wales, which needs fewer workers.

Unite said 1,500 of its members based in Port Talbot and Llanwern started industrial action on Tuesday, warning that strikes will be held if the company does not row back on its plans.

Unite general secretary Sharon Graham said: “Tata’s workers are taking this industrial action because they know the company’s claim that jobs cannot be retained in south Wales during the transition to green steel is a lie.

“They are standing up and fighting for a better future, one in which Tata’s British business can take full advantage of the coming green steel boom and not be sacrificed to benefit its operations abroad.

“The current government have backed Tata’s disastrous deal for Britain without even getting any job guarantees.

“But in less than a month, Tata will almost certainly be dealing with a new political reality. Labour has told Tata to wait for the £3 billion steel investment fund, a commitment secured by Unite. That is what it must do. Unite will use every weapon in its armoury to ensure that it does.”

A Tata spokesperson said: “Of the 4,500 Tata Steel UK employees in Port Talbot and Llanwern, 1,366 Unite members were balloted, 857 voted and of those 468 members voted for industrial action including strike action.

“We have challenged the legality of their ballot process on multiple occasions and our position is that their industrial action is unlawful.

“Furthermore, through extensive negotiations with unions the company twice substantially improved our support offering for affected employees – the most generous package in our history – we would have expected Unite to put this offer to their members.

“Having now received notice of Unite’s industrial action, we have regrettably reverted our employee support package to closer to our standard terms.

“We have written to our workforce to make sure that any employee subject to Unite’s notice and considering taking part in any industrial action is fully aware and understands that their contract of employment, associated collective agreements, and job description, as well as terms implied by established custom and practice and/or by law, may require them to work additional hours and continue to support and cover activities as outlined in Unite’s notices of industrial action.”

Community and the GMB union also have members at Tata, but have not announced any industrial action.

Alun Davies, national officer for Steel at Community, said: “Community and GMB senior officers met last week and have made the decision not to undertake any industrial action before the General Election.

“If the Labour Party wins the General Election it has said that it will hold emergency talks with Tata on the future of Port Talbot and the downstream sites as soon as possible.

“We welcome this and now feel it is important to wait for the completion of that process before initiating any significant course of action.”