Tasmania's Premier has personally called the head of the Education Department to express his anger after a leading parenting author and educator was gagged from speaking out against the State Government's controversial education changes.

Steve Biddulph was due to present at a conference in Tasmania's north-west this weekend.

In a social media post that has since been removed, he detailed his surprise after being asked by the Department of Education not to talk about the Government's plan to lower the school starting age.

"With just a week to go, I received a shock, a contract in the mail, requiring me to sign an agreement not to discuss any topic that could be perceived as political or partisan," he wrote. "I asked what this meant and was told, in writing, that it meant I was NOT TO DISCUSS SCHOOL STARTING AGE or related issues during my presentation. "It was a legal and binding commitment. "Ethically, I could not sign and I let the organisers know this."

Mr Biddulph withdrew from the event.

"I conveyed also that I thought it very wrong that discussion was being supressed in the community, and the idea that a presenter would be gagged in this was something very bad for the state," he said on Facebook.

The education plan was fiercely opposed by many parents and educators when it was announced, prompting the Government to make the school starting age change voluntary.

Premier Will Hodgman today distanced himself from the move.

"It was not instigated by the minister, it was not instigated by myself, it was done by the department," he said.

"It's unacceptable, it's embarrassing and shouldn't happen again."

The Premier said he was informed on Tuesday and had since called the head of the Education Department to express his concerns.

"I think it's entirely unacceptable, I think it's bang out of order," he said.

"I myself have been in contact with the secretary of the Department of Education to understand how such a thing could occur.

"I'm advised that it is unusual, it's not the sort of thing that happens and nor should it."

'Culture of secrecy' in Tasmanian Government

Labor leader Bryan Green said it was a move designed to silence potential criticism.

"We know that there is secrecy within this Government, it's rife," he said.

"The Government is so shy that a guru, a world-renowned expert is effectively gagged from speaking his mind about early childhood, it's just ridiculous."

Mr Green said the Premier was shifting the blame to the Education Department.

"In government, you have to take responsibility for actions, and here is the Premier, so twitchy about our reputation, now as a result of this scandal actually calling the secretary of the department to essentially blame them completely," he said.

"I'm surprised he would do that because it's a culture, it's a culture within this Government of secrecy."