Under the new decision, public sector bodies are to be encouraged to buy British steel for construction projects in an effort to help save the industry.
The government said councils and NHS trusts will be asked to consider the economic impact of buying from abroad.
Business Secretary Sajid Javid said he was determined to ensure a sustainable future for the British steel industry and find a solution that supports workers.
The government's decision comes after Tata Steel announced last week that it was selling its loss-making UK plants, putting thousands of jobs at risk.
The unions said the government's decision was "a small step in the right direction" but the measure should have been in place already.
Guidelines were introduced last year requiring central government bodies to take into account the "true value" of British steel.
Contractors working for the public sector will also be required to advertise their requirements for steel so that UK firms can compete for the business.
Authorities hope local steel firms could supply steel for huge projects like the 55-million-pound high-speed rail link, which will need some two million tonnes of steel.
It comes after heavy criticism of ministers for failing to take more effective action to prevent the "dumping" of cheap Chinese steel, seen as one of the key reasons for the problems in the UK steel industry.
Roy Rickhuss, general secretary of the Community trade union, said the announcement was "a small step in the right direction" but said steelworkers "will be shocked to discover that these measures were not already in place".
"These are bread-and-butter policies that should have been providing opportunities to UK steel producers already," he said.
