Donald Trump's proposed increase in steel tariffs will have a "significant impact" on the UK, the industry trade body has warned.
The US President has set out plans for an import tax on steel at 25% and 10% for aluminium.
Mr Trump said US steel and aluminium had been "decimated" by "unfair" trade policies, and insisted he would not let America be "taken advantage of any longer".
The US is a significant export market for the UK and a hike in tariffs would have an affect on the British steel trade, the industry warned.
"It would have a significant impact if it did go ahead," Richard Warren, head of policy at UK Steel told BBC Radio 4's Today programme.
Mr Warren said the US accounted for around 15% of UK steel exports generating £360 million worth of products.
Further details on Mr Trump's plans are expected next week.
Mr Warren said: "This would be a unilateral, and extremely blunt, approach to what is a complex global problem of overcapacity in the steel sector.
"Whilst we all too well understand the frustrations of the US sector, measures such as these smack of short-termism, protectionism and would be rife with unintended consequences for global trade and for the users of steel in the US.
"These measures would seriously undermine our ability to compete in this market.
"Equally there is significant apprehension about the indirect impacts of these measures in the form of steel trade diverted away from the US to other markets, such as the UK.
"In short, these measures would cause serious damage to the prospects of many steel producers here.
"Whilst performed under the guises of national security, whichever way you look at it the UK exports of steel into the US are clearly no threat to US security and pose no threat the health of the US steel sector. We are one of its oldest and closest allies. We trust the UK Government would push for and fully support a robust response from the EU.
"If next week's official announcement does reveal the worst, there is a strong message here for the UK Government as well. In its imagined post-Brexit role as the vanguard for global free trade, it must remember that not everyone is on the same page and not everyone is playing by the same rules.
"Whilst we have to resist any urge to mirror such protectionist moves, we must at the same time be clear-eyed and equip ourselves with tools to respond effectively and protect our interests when necessary."
Unite union national officer for steel Tony Brady said: "US tariffs on UK steel would be devastating for the British steel industry and the thousands of workers who have battled for its survival alongside their trade unions.
"Any tariffs imposed on UK steel by President Trump on a scale that is being mooted would be misguided and deprive US manufacturers of some of the most specialist steel in the world.
"The dumping of cheap Chinese steel into the UK took our world-class British steel industry to the precipice because of the Government's inaction.
"Government ministers and Theresa May must back Britain's steelworkers and manufacturing communities by securing assurances from President Trump that they will not be caught up in a global tariff war between the US and countries such as China."
The European Union has indicated it could retaliate, potentially starting a trade war with the US.
European Commission president Jean-Claude Juncker said: "We will not sit idly while our industry is hit with unfair measures that put thousands of European jobs at risk.
"I had the occasion to say that the EU would react adequately and that's what we will do.
"The EU will react firmly and commensurately to defend our interests. The Commission will bring forward in the next few days a proposal for WTO-compatible counter-measures against the US to re-balance the situation."