WASHINGTON—President Donald Trump has ordered White House aides to draft a tax plan that slashes the corporate tax rate to 15%, even if that means a loss of revenue, according to people familiar with the directive.

During a meeting in the Oval Office last week, Mr. Trump told staff he wants a massive tax cut to sell to the American public, these people said. He told aides it was less important to him that such a plan could add to the federal budget deficit, though that might make it difficult to sell to GOP lawmakers who are...