Union members of sites in Wales, Scotland, South Yorkshire and Teesside all supported Tata Steel's new proposals, which included major investment plans and job security.
Tony Brady, national officer for union Unite, said the company must now honour its previous commitments.
"Nothing less would be a betrayal and add to the deep mistrust that steelworkers now have for the company," he said.
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"The UK government in Westminster must also repay the sacrifices and the commitment shown by steelworkers to their industry by stepping up to support steel and secure its future. Recent talk of steel being a low priority for UK government ministers in Brexit negotiations is shameful.
"The UK government must now work in lockstep with the Welsh government and put steel at the heart of a manufacturing industrial strategy which ensures UK steel is used in all major infrastructure and defence projects."
Dave Hulse, national officer for GMB, added: "Now that steelworkers have done their bit, it is time for the government to step up and do theirs. Thousands of skilled jobs rely on steelmaking and the industry supports the whole UK manufacturing sector.
"Instead of insulting steelworkers by classing their industry as a 'low priority', the government must set out a strategy for steel that recognises it as a high priority for investment and innovation."
(LM/MH)
