Tassal referred to Senate over allegations

The Greens have referred salmon farmer Tassal to the president of the Senate over allegations the company attempted to constrain a Senate inquiry witness.

Salmon farmer Tassal has been referred to the president of the Senate amid allegations it attempted to influence a Senate inquiry witness.

The allegations aired by Four Corners on Monday claim the company wrote to witness Warwick Hastwell, owner of Dover Bay Mussels, to remind him of his "obligations not to make disparaging statements" ahead of his scheduled appearance before a Senate inquiry.

Mr Hastwell later backed out of giving evidence to the inquiry into the fishing industry.

Greens senator Peter Whish-Wilson says the matter has been referred to Senate President Stephen Parry.

"The Parliamentary Privileges Act 1987 and the Senate standing orders set out clearly that it is contempt of the Senate for a person or company to use intimidation, threat or inducement in relation to another person's evidence before a committee," he said on Thursday.

"I am concerned by the allegation that Tassal may have sought to constrain a witness in what they could or couldn't present to a Senate inquiry."

Tassal insists the Four Corners program on its farming practices "misled consumers, investors and the Tasmanian community".