President Trump has demanded that Americans boycott Goodyear after the tyre company banned staff from wearing political attire in the workplace.
The US leader clearly saw the rule as an attack on his “Make America Great Again” (MAGA) slogan as the country gears up for another bitterly divisive presidential election in November.
As is customary, Mr Trump used his Twitter account to go on the offensive.
He wrote: “Don’t buy GOODYEAR TIRES – They announced a BAN ON MAGA HATS”.
The tweet followed a report by WIBW television in Kansas, citing information from an anonymous Goodyear employee, that suggested Black Lives Matter, lesbian, gay, bisexual and transgender pride messages were seen as acceptable by the company, though politically affiliated slogans were not.
Goodyear, which insisted its policy applied to any party’s campaign material, endured a 4% fall in its share price after Mr Trump’s call for a boycott.
It is the largest tyre company in North America, accounting for almost a quarter of annual sales in the United States.
Last year, it reported revenues of $15bn (£11.4bn).
Goodyear explained that it asked workers to refrain from “workplace expressions in support of political campaigning for any candidate or political party as well as similar forms of advocacy that fall outside the scope of racial justice and equality issues”.
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The company said in a statement: “To be clear on our longstanding corporate policy, Goodyear has zero tolerance for any form of harassment or discrimination.”
Goodyear was founded more than 120 years ago in Ohio, a battleground state in the presidential election.