The leaders spoke for the first time since the announcement in a 30-minute call and agreed to discuss the issue further at the G7 summit in Canada later this week.
Trump has infuriated European Union members, Canada and Mexico by imposing tariffs of 25 percent on steel and 10 percent on aluminium, ending months of uncertainty about potential exemptions and suggesting a hardening of the US approach to trade negotiations.
"The prime minister raised the US decision to apply tariffs to EU steel and aluminium imports, which she said was unjustified and deeply disappointing," a spokesman for the prime minister told reporters.
"She said the US and UK and EU are close national security allies and we recognise the importance of the values of open and fair trade across the world. The prime minister also underlined the need to safeguard jobs."
The EU threatened tariffs on Harley Davidson motorcycles and bourbon, measures aimed at the political bases of US Republican legislators.
"It is right to seek to defend our domestic industries from both the direct and indirect impacts of these US tariffs. The response must be measured, and proportionate," Fox told parliament.
During the call, May also announced her support for Trump's plan to meet North Korean leader Kim Jong Un in Singapore next week.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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