Prime Minister Malcolm Turnbull says former trade minister Andrew Robb did not approach him about his new role with the Chinese company that now operates Darwin Port.

Mr Robb has become a "high-level economic consultant" with the Landbridge Group, which was awarded a 99-year lease over the Port of Darwin last year in a $506 million deal with the Northern Territory Government.

Mr Turnbull praised Mr Robb's work in Parliament, but confirmed the former trade minister did not inform him of his new job.

"He has not raised this particular role with me, no," he said.

A September statement from Landbridge, translated for the ABC, quotes board chairman Ye Cheng as saying that in order for Landbridge to achieve its global goals "it will be necessary to draw on experts such as Mr Andrew Robb who have global vision and global influence".

Former ministers are banned from lobbying the Australian Government for 18 months, meaning Mr Robb would have to wait another year before he can advocate for the Landbridge Group on trade matters.

Foreign Minister Julie Bishop today defended Mr Robb's decision, telling the ABC he should be allowed to have a post-Parliament career.

"Andrew has said he's aware of the ministerial code of conduct and he'll abide by it," she said.

Opposition ask for proof rules are being followed

But Labor's Wayne Swan said Mr Robb was "flouting" the code of conduct.

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In a tweet posted this morning, Mr Swan said Mr Robb and Ian Macfarlane, who was recently appointed as chief executive of the Queensland Resources Council, were "flouting Turnbull's Ministerial Code of Conduct".

Chairwoman of the Senate's Finance and Public Administration committee, Labor's Jenny McAllister, said the Opposition wanted proof the rules were being followed.

"Mr Robb and Mr Turnbull need to demonstrate that they are committed to the statement of ministerial standards and committed to upholding them," she said.

"We need to be certain that they're not using sensitive information they had access to as a minister to benefit their company and we also need to be sure all the proper rules are being followed, especially when it comes to lobbying ministers or public servants.

"These are the questions Mr Turnbull really needs to satisfy the Australian public about."