The call comes after Mr Robert broke his silence on the Sunland affair, saying any suggestion that he supported the Gold Coast company in exchange for donations are "incorrect and scurrilous".

But Mr Robert has not denied the speech he delivered to Parliament defending Sunland in a legal dispute was substantially written by company lobbyist Simone Holzapfel, saying it was important to be "precise" with his language.

"Four years ago I stood up as a local member and gave a short speech in Parliament because I felt Sunland were receiving one-sided criticism in the media. Following two earlier speeches delivered by a Senator colleague that I also felt were one-sided, I believed that if one side of the issue could be aired in Parliament, the other side could be as well. That is only fair," he said in a statement on Thursday.

"I was informed by various sources.

"Due to the complexities of the issues involved it was important to be precise with language, I delivered my own speech."

Making his first public comments on the issue, Prime Minister Malcolm Turnbull did not offer a defense of his back bencher.

"That speech has been on the public record, the donations that were made by a property developer have also been on the public record and disclosed," he said.

"He set out all those facts and I refer you to them."

Pointing to Mr Turnbull's comment, Labor leader Bill Shorten ramped up his attack on Mr Robert on Thursday afternoon, saying he was "surprised" by the Prime Minister's handling of the matter, given the swiftness on which the government seized on the Sam Dastyari matter.

"When the Prime Minister was asked about the conduct of a chairmen of a senior parliamentary committee which Stuart Robert chairs, he said 'oh just read his statement'.

"Now I know Malcolm Turnbull blames someone else for the census, blamed someone else for the backpacker tax, changed his views and watered down his views on superannuation, but he can't hide behind Stuart Robert," he said.

"Malcolm Turnbull has to decide does he back Stuart Robert, or will he sack Stuart Robert?  Will he back him or sack him? That's the question which Mr Turnbull has to answer."

Shadow attorney-general Mark Dreyfus says Mr Robert's position as chair of Parliament's Committee on Treaties is untenable.

"This is an important role which oversees major trade deals and extradition treaties with other nations," he said.

"It demands someone of the highest integrity and impartiality to fill that role – Mr Robert is clearly not the right person for the job."

The job adds almost  $32,000 to his backbencher salary of $199,000.

Former Labor MP Craig Thomson was forced to stand down as chair of the lower house Economics Committee in August 2011 as he was investigated for misusing Health Services Union funds.

Fairfax Media revealed this week that seven sections of Mr Robert's short speech came from a briefing note prepared by Ms Holzapfel, a former Tony Abbott staffer who now runs a Gold Coast communications company.

The briefing note and speech defended Sunland in its dispute with Australian businessmen Marcus Lee and Matthew Joyce, who were locked in up Dubai for five years as part of a land dispute with the company.

Eight months later Sunland donated $25,000 to the Queensland Liberal National Party. Sunland has denied it got or expected any benefit from the donations.

Mr Robert - who has until refused to comment on the matter - says it should be no surprise he supports "responsible development".

"Sunland have played a major role in building our city over the last three decades, including much of my northern Gold Coast electorate," he said. "To draw a link between an issue I supported as a local MP and an unrelated and fully disclosed donation over eight months later is an outrageous and offensive assertion."

Mr Robert says Sunland have also made "extensive donations" to the Queensland Labor Party. However disclosure returns show Sunland has not donated to Labor for more than a decade.

Ms Holzapfel has also donated $114,000 to the LNP and Mr Robert's own fundraising vehicle, the Fadden Forum.

The Australian reported on Thursday that Ms Holzapfel had lobbied the office of then-opposition leader Tony Abbott to to tone down its support for Mr Lee and Mr Joyce. The approach was made the same day Mr Robert delivered his speech to Parliament, the newspaper said.

Mr Robert's links to Sunland are being investigated as part of a Queensland corruption inquiry looking into claims of dodgy donations around the Gold Coast City Council election in March this year.

In particular, the Fadden Forum is being examined after it was used to bankroll two candidates in the Gold Coast City Council elections.

Kristyn Boulton and Felicity Stevenson - who both worked for Mr Robert - were given $30,000 each to run at the March poll but their LNP links were not disclosed until months later. They both ran as independents. Ms Boulton was elected to the council while Ms Stevenson returned to Mr Robert's employ.

Mr Robert was sacked from Mr Turnbull's frontbench in February over a controversy involving Liberal donor Paul Marks.

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