The US Supreme Court  heard arguments Wednesday concerning a man who wanted to print T-shirts emblazoned with the suggestive slogan "Trump too small," in a case that weighs both trademark rights and freedom of expression.

Former president Donald Trump, who is not involved in the case, is otherwise tied up in a number of legal disputes, including a civil trial underway this week in New York for fraudulently inflating the value of his business empire.

In the case before the Supreme Court, California lawyer Steve Elster tried to trademark the sexually suggestive phrase and print it on T-shirts. But his bid to register the slogan was rejected by the US Patent and Trademark Office because he did not have Trump's written consent to use his name.

A federal court of appeals disagreed, ruling that this decision was a violation of Elster's free speech rights under the First Amendment.

The federal government asked the Supreme Court to intervene, arguing that a refusal to trademark the slogan did not prohibit its use, but only meant it wasn't protected under intellectual property law.

The phrase "Trump too small" arose from the 2016 Republican presidential primaries during which Senator Marco Rubio of Florida said Trump had "small hands."

Trump, who frequently referred to Rubio during the campaign as "Little Marco," responded by saying "If they're small, something else must be small. I guarantee you there is no problem."

Elster's attorney, in a brief, said the "Trump too small" phrase is "political commentary" and while it does involve a double entendre it is meant to convey his client's view of "the smallness of Donald Trump's overall approach to governing as president of the United States."

"Even if Mr Elster can't register the mark 'Trump too small' he can sell shirts with that slogan," government representative Malcolm Stewart argued before the Supreme Court's nine justices.

The law "simply restricts Mr Elster's ability to assert exclusive rights in another person's name," he said.