UPDATED 1.03pm: The union for senior doctors says a District Health Board is trying to intimidate one of its staff into silence.

Dr Chris Cresswell publicly aired his views that the trade deal would have a huge impact on the price of medicine.

His union boss, Ian Powell from the Association of Salaried Medical Specialists, reports he's now been called in to a code of conduct meeting tomorrow by the DHB.

"They're clearly angry, but I'd say it's worse than that. I think they're obsessive, because there are other specialists in other parts of the country who have spoken out on their concerns about the Trans Pacific Partnership Agreement."

Powell said the DHB's essentially threatening disciplinary action, which is a ridiculous reaction to what should be free expression.

He said the DHB's collective agreement specifically includes protection for the right of doctors to engage in public debate on matters related to their expertise.

"Dr Cresswell, like other specialists in our public hospitals, actually does have a right to speak out publicly on matters to do with their professional expertise and experience."

The Council of Trade Unions Secretary Sam Huggard is surprised the DHB wanted to discipline Dr Cresswell.

He said it's the opposite to the attitude of other DHB's towards the TPP.

"Across the country Dr Chris Cresswell is not out of the ordinary, in fact his views are in the mainstream of what the medical profession's views are on the TPP right now," Huggard said.

"We're fairly confident that once the DHB realised that they're the outlier on this and most other DHB's aren't playing this top muzzling role, it should resolve itself fairly quickly."