PM needs to pull Bernardi into line: Labor

Labor has called on the prime minister to pull Liberal backbencher Cory Bernardi into line over his "campaigning" for US presidential hopeful Donald Trump.

The conservative senator is on a three-month secondment to the United Nations in New York as a parliamentary observer.

But Labor's Penny Wong has accused him of using the taxpayer-funded post to support Trump.

Senator Bernardi has openly backed the Republican candidate - the only person he follows on Twitter - while criticising the Democratic candidate Hillary Clinton.

Although he insists he's not a cheerleader for Trump, he told Sky News on Thursday the Republican has a "better chance to fix what's wrong with America".

It follows similar comments on social media and other outlets in recent days.

Senator Wong said Malcolm Turnbull "needs to pull Bernardi into line".

"He's not in NYC to campaign 4 Trump. He's representing the Aust Parlt. Funded by the taxpayer," she tweeted on Thursday.

Senator Bernardi acknowledged in March when he won the ballot to go to the UN he needed to stay on script, telling the ABC: "I've already been told there's no freelancing at the UN."