Theresa May has told Donald Trump that US tariffs on EU steel are “unjustified and deeply disappointing”, speaking by phone with the American president for the first time since the levies were imposed last week.

Downing Street said the 30 minute call on Monday afternoon was constructive and stressed the close national security relationship between the two countries. May will not push for a UK exemption to the new US border tariffs of 25% on EU imports of rolled steel and 10% on aluminium as the UK will join the bloc’s push for European exemption.

“The PM said that the US, UK and EU are close national security allies and we recognise the importance of the values of open and fair trade across the world,” May’s spokesman said.

“The prime minister also underlined the need to safeguard jobs that will potentially be affected by this decision. They agreed to discuss this, and wider issues of free and fair global trade, further at the G7 summit later this week.”

The EU, Canada and Mexico were granted exemptions when Trump imposed the tariffs in March, saying a reliance on imported metals threatened national security. Last week however, US commerce secretary Wilbur Ross said the US had made insufficient progress with its allies to reduce America’s trade deficit, and lifted the waiver.

May’s spokesman stressed that the UK was not trying to strike its own deal with Washington. “We are members of the European Union and we have been clear that we and our EU allies are seeking an EU-wide exemption,” he said.

In a speech on Tuesday, Jeremy Corbyn will suggest the prime minister’s hesitancy to use stronger terms to condemn Trump’s actions was May trying to “appease” the US president in the hope of getting a better trade deal with the US in the wake of Brexit.

The Labour leader will tell the GMB union that the move to impose further steel tariffs would risk hurting workers in America and around the world.

“The Tories are too weak to stand up to the powerful, and too in hock to them even if they wanted to. Theresa May is appeasing Donald Trump in the hope of getting a race-to-the-bottom trade deal with the US after we leave the European Union. The Trump trade tariffs show that’s a Tory pipe-dream,” he said.

Corbyn will say that US workers have long suffered from a “completely rigged system” that shifts more power and wealth to a tiny financial and political elite.

“Trying to hold back the tide with one hand and giving eye-watering handouts to the super-rich with the other is no substitute for a government taking a proactive role in modernising and upgrading industry,” he will add.

Speaking in the House of Commons earlier however, the international trade secretary, Liam Fox, said he hoped once the UK had left the EU, “we’ll have no problems with a UK exemption.”

He suggested he was cautious about some of the retaliatory tariffs under discussion at the EU, including classic American products such as Levi’s jeans, bourbon whiskey, cranberries and peanut butter.

“We still want to see what the measures themselves are, specifically we have been talking to the Irish government about the issue of bourbon being on the list because of the potential implications for the Scotch whisky industry and the Irish whiskey industry,” he said.

The shadow international trade secretary, Barry Gardiner, said the issue must be given a formal place on the agenda at the forthcoming G7 summit in Canada. “The UK must insist that this matter is given a high priority on the formal agenda and not relegated to the sidelines,” he told the Commons. May is expected to discuss the tariff with Trump at the summit this week.

Gardiner said there would be “no winners” if the EU and the US entered a full-scale trade war. “Only President Trump has said he believes he can win one. The UK and the EU must stand up to this behaviour and restore the rules-based system,” he said.

MPs called for even tougher retaliatory steps, with Labour MP John Mann suggesting the UK impose “golf tariffs” aimed at Trump’s properties.

“Giving into this, the only language that Trump understands, is people fighting back, and it’s about time this country fought back,” he said. “We can do it. Golf – he likes golf – let’s have some golf tariffs on golf owners in Scotland. Let’s bring them in immediately and stand up for our steel communities and our steel workers instead of this rubbish about how we can do nothing about it. Fight him.”

Fox said his suggestion was “a tirade of nonsense” but added the UK did not have the authority to set out its retaliatory measures. “When we leave the European Union we will have greater freedom to do so. But I say in all seriousness that escalation is not what we require – we need a proportionate response done calmly, with time to give the United States some reflection to change its mind.”

Commenting on the phone call between May and Trump, White House spokeswoman Sarah Sanders said: “The president feels very confident in his decision and will continue to make sure that the unfair trade practicies that have gone on for decades will not continue and that he is protecting the interests of American workers and American business.”