Washington DC - President Donald Trump issued an executive order Thursday prohibiting companies doing business with the federal government from having policies meant to combat racism or sexism in the workforce.

The order, to come into effect in 30 days, is Trump's latest move against diversity, equity and inclusion (DEI) policies, a series of often decades-old measures meant to combat racism and sexism across the US.

The Republican president and many of his hard-right supporters claim DEI measures constitute a form of reverse discrimination.

"My Administration has made significant progress in ending racial discrimination in American society, including so-called 'diversity, equity, and inclusion' (DEI) activities," Trump wrote in the order.

He claimed that DEI policies also raise costs for employers, who then pass those on to the federal government when bidding for contracts.

Companies now hoping for government contracts will have to include on their contracts a seven-paragraph clause pledging, "The contractor will not engage in any racially discriminatory DEI activities."

Shortly after re-entering the White House for a second term last January, Trump put US federal employees working in diversity offices on paid leave after ordering the programs shut.

In August, his administration said it would "review" certain displays and exhibitions at the Smithsonian museums in Washington, looking to remove "divisive or partisan narratives" as part of his war on "wokeness."