Steelworkers in three unions have voted in favour of proposals that will see their pensions benefits cut.
The proposals will see Tata Steel pump £1bn into the sprawling Port Talbot steelworks in exchange for workers accepting changes to their pension schemes.
More than 70 per cent of the steelworker members of GMB, Community and Unite unions decided to accept a the creation of a "mirror" pension scheme that will result in reduced retirement benefits, with future payments linked to the consumer price index of inflation, rather than the faster rising retail price index.
British Steel Pensions Scheme members will then be given the choice of switching over to the new scheme, with the small number of workers who would benefit more from protections offered by the Pensions Protection Fund able to opt out.
The vote has been described as "make or break" for the future of the British steel industry, with observers questioning Tata's commitment to the UK if it had been unable to secure reform.
The future of the Port Talbot works have been in doubt for almost a year, with the Indian firm first revealing sale plans last march in the face of falling global steel prices.
That prompted then-business secretary Sajid Javid to step in, and offer government support for any buyer, before Tata later took the operation off the market in the aftermath of the summer's Brexit vote, to explore a now-stalled joint-venture with Thyssenkrupp.
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Roy Rickhuss, general secretary Community, said: "Steelworkers have taken a tough decision and have shown they are determined to safeguard jobs and secure the long-term future of steelmaking.
He added: "We now expect Tata to make good on their promises and deliver the investment plan for the whole of their steel business."
A spokesman for the government's business, energy and industrial strategy department said: “It is testament to the commitment of its workforce that they are willing to work so constructively with the owners to secure the future of the plant.
"The government will play its role in supporting the steel industry to help deliver a sustainable future.”
Aberavon MP Stephen Kinnock, whose constituency includes the Port Talbot steelworks, said the loss of the steelworks would have been "unimaginable".
“Tata must now uphold their pledge to retain the two blast furnaces in Port Talbot, avoid compulsory redundancies, placing the UK workforce on the same footing as their colleagues in the Netherlands, and bring forward the £1bn investment plan that will go a long way towards building the competitiveness and productivity of Port Talbot and the downstream sites.
"If fulfilled, the package voted on today should secure the future for Port Talbot."