Indian steel giant Tata has published details of the redundancy offer made to thousands staff at Port Talbot which it says is the most generous in its history. However the firm has threatened to withdraw the offer if workers, who are being balloted on strike action by three unions, take industrial action in the coming months.

Tata workers taking redundancy will receive 2.6 weeks of salary for every year worked up to a maximum of 25 years, meaning the longest-serving staff will receive the equivalent of 65 weeks wages. The minimum any worker taking redundancy will be paid is £12,500, regardless how long they have worked for the company.

On top of that, staff being made redundant will receive an additional £5,000 provided their attendance level is 96% or higher in the last four months of their employment. Tata is seeking to make 2,500 redundancies across the UK in the next 18 months, with a reported 1,900 roles going at Port Talbot steelworks when the two blast furnaces shut down later this year as planned.

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However, Tata told employees in a letter from chief executive officer Rajesh Nair that these "enhanced" redundancy terms "are conditional upon there being no industrial action in the business". He said the offer was "the most favourable financial package of support our business has ever offered".

This comes as three unions representing Tata staff ballot for industrial action. Tata's sites in Wales affected by the redundancies include Port Talbot, Llanwern and Trostre.

The Community union has around 2,700 members across the Port Talbot, Llanwern and Trostre sites. Their ballot opens on April 11 and it will be open for a month.

A Community spokesman said: "We won't be bullied. Our priority is fighting for jobs and that's exactly what we're going to do - this is about the future of Port Talbot and generations of steelworkers to come."

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National officer for steel at Community Union, Alun Davies, said it did not believe the company were "serious about engaging" and that they had "little choice than to put this issue to our members and ask them if they want to take the next step towards industrial action".

Unite's ballot is already open with its flags and advertisements boards in place outside the entrance. They say they their ballot is of 1,500 workers at the Port Talbot and Llanwern sites with the ballot closing on the day the Community ballot opens.

GMB, the union with the smallest representation at Tata, is opening its ballot over industrial action on April 4, and that closes on April 25.

The Unite result is expected to be made public shortly afterwards, and the union has said industrial action could begin before the end of April. The result of the Community and GMB ballots will not be known until mid-May but there is an expectation all unions would take action at the same time.

Tata says the reason for its shift to electric arc steelmaking and shutting down the blast furnaces making virgin steel at Port Talbot is to "reverse more than a decade of losses and transition from the legacy blast furnaces to a more sustainable, green steel business". The UK Government has agreed to give the steel giant £500m and the company itself will put £750m towards the £1.25bn project. The Welsh Government, UK Labour and unions, oppose the plans. An alternative plan backed by two of the unions, Community and the GMB, has been rejected by the company who say they are losing £1m a day and that theirs is the only option.

Changes are already happening on site. On Wednesday, March 20, Tata closed the coke ovens, which had been open at the Port Talbot site since 1981, because of "significantly deteriorating operational stability". The closure of the coke ovens will also close the neighbouring by-products plant. Those whose jobs are impacted are being offered other roles at the site but unions say it was a sign of betrayal.

A statement from Unite the union said although the coking ovens were known to be in a state of disrepair, Tata had not indicated to unions, they say there was any risk of imminent closure.