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A Liberal senator has apologised for "meowing" at Finance Minister Penny Wong during a Senate hearing.

David Bushby made the feline cry during a heated row between the minister and coalition senators on Wednesday.

The catty response drew a sharp rebuke from Senator Wong.

"Why do you meow when a woman does that?" she asked Senator Bushby.

"It's extraordinary. Blokes are allowed to yell, but if a woman stands her ground, you want to make that sort of comment. It's schoolyard politics."

Senator Bushby later issued a written apology to the minister.

"My reaction to Senator Wong occurred during a robust debate about calling the secretary of treasury to appear before estimates," he said.

"I am sorry that Senator Wong has felt offended by my reaction."

Senator Bushby said he had tried to call the minister to apologise in person.

Senior coalition frontbencher Joe Hockey also rebuked the senator, saying his behaviour was not acceptable.

"Obviously it's not acceptable and I understand the senator has contacted Penny Wong to apologise," he told reporters.

Asked if he rejected sexist attitudes in the coalition, Mr Hockey said: "Absolutely. I don't think anyone would ever suggest that I was sexist or have sexist attitudes."

Treasurer Wayne Swan said the behaviour of Senator Bushby and lower house coalition MPs was becoming feral.

"I think the finance minister was absolutely right not to put up with the rudeness and sexist behaviour of (Opposition Leader) Tony Abbott's goons," he said.

Coalition senators were angry that Treasury secretary Martin Parkinson was not present when officials from his department's fiscal group appeared before the Senate hearing on Wednesday morning.

Senator Wong said that it was not normal practice for the Treasury secretary to attend all parts of estimates hearings.

That had been the case equally under the Howard government, she said.

Dr Parkinson is scheduled to appear before the Senate's economic committee on Thursday.