Documents produced by the Greens also purported to show Mr Taylor is a shareholder in the company at the centre of the investigation. However, officials from the Department of the Environment and Energy said he had not been briefed on the investigation.

Under questioning by Greens senator Janet Rice, the department's chief compliance officer Monica Collins confirmed the department was investigating potentially illegal breaches relating to a 30-hectare paddock sprayed with herbicide. The paddock, at a property in southern NSW, allegedly contained native temperate grasses - considered an endangered ecological community under federal environment laws.

Officials declined to discuss the specifics of the investigation. But they confirmed that Jam Land Pty Ltd was the company at the centre of the investigations, and Richard Taylor, the brother of the minister, was a director of the company.

Senator Price produced a document she said showed Angus Taylor was a shareholder of Gufee Pty Ltd, which was in turn a shareholder in Jam Land.

The department's secretary Finn Pratt said he was "not aware the minister is a shareholder, I do not know that information and I can be very clear, Minister Taylor has never raised the issue with me".

Asked how the department was managing the potential conflict of interest, officials said neither Mr Taylor nor Environment Minister Melissa Price, with whom he shares oversight of the department, had been briefed on the investigation, and Mr Taylor did not have responsibilities in the area.

Senator Rice cited a submission made by Richard Taylor to the department's review of how environment laws affect the agriculture sector. His submission called for changes to make the laws more simple and compatible with broadscale agriculture and best-practice weed control.

A report on the review was handed to Ms Price in November last year. Officials said the briefing did not cover individual submissions.

The department's assistant secretary Dean Knudson told the hearing that some recommendations made by Richard Taylor reflected the broad view of farmers who felt "the Act is actually holding them back from doing reasonable weed management in an effort to protect something that quite frankly might be of marginal ecological value".

Comment has been sought from Angus Taylor's office.

The Wilderness Society federal policy director Tim Beshara said Ms Price must clarify how she and the department managed the potential conflict of interest "both in the compliance action against Minister Taylor's family business and how they dealt with that company's submission to the review of the EPBC Act."

"If a minister involved in financial regulation had held shares in a family company which was under investigation for a law breach, a conflict of interest would have to have been declared and firewalls put up. The same should have happened here," he said, adding that the department should have declared the potential conflict rather than wait for it to emerge at Senate estimates.

- SMH/The Age