Greens co-deputy leader Larissa Waters has called on Nationals senator Barry O'Sullivan to explain why he queried her marital status during Question Time yesterday.

The remark came after Senator Waters was forced to rephrase a question about whether Catholic Government MPs, including the Prime Minister, would respond to the Pope's call for urgent action on climate change.

Senate president Stephen Parry told Senator Waters it was out of order to refer to other Senators' religion during debate.

The Government's acting leader in the Senate, Attorney-General George Brandis, described her question as "disgusting".

Senator Waters said her identification of Government MPs as Catholic was not meant disparagingly.

Amid the protests from Coalition senators, Queensland LNP senator Matt Canavan can be heard calling Senator Waters a "bigot", but withdrew the comment.

As Senator Waters reworded her original question, Senator O'Sullivan can be heard asking: "You're married aren't you?"

"No, I'm not and that's an irrelevant question, my marital status has nothing to do with this chamber," Senator Waters replied.

She later described the question as "inappropriate and bizarre".

"Senator O'Sullivan really needs to explain what on earth he was referring to," she said.

"This [remark] is more bizarre than sexist, but I don't recall a male senator's marital status ever being called into question."

Senator O'Sullivan did not respond to the ABC's requests for comment.

Late last night, Senator Canavan gave a speech in which he apologised for what he called an "undue outburst", and then attacked Senator Waters, saying her reference to Catholic MPs was "religious dog-whistling".

"The Greens are massive hypocrites," he said.

"The Greens speak of human rights but then mock people of certain religious beliefs.

"As a practicing Catholic, I am fed up with how Catholics are portrayed by Senator Waters and sections of the media."