Checking Facebook and liking a post critical of the Government could be enough to see public servants facing disciplinary action, under new guidelines that also say employees may be held accountable for comments other people make on their Facebook pages.

The Australian Public Service Commission's social media guidelines were updated this morning, reinforcing the requirement that public servants appear impartial in their roles.

The rules give particular weight to public servants criticising their own departments, but their coverage of sending private emails, liking Facebook posts, and failure to delete posts made by other people have sparked the ire of the public sector union.

A frequently asked questions section of the page outlined the breadth of the updated guidelines.

"If you 'like' something on a social media platform, it will generally be taken to be an endorsement of that material as though you'd created that material yourself," it reads.

"'Sharing' a post has much the same effect.

"Doing nothing about objectionable material that someone else has posted on your page can reasonably be seen in some circumstances as your endorsement of that material."

The guidelines also state criticising parliamentarians on both sides of the aisle could also breach the code.

"Criticising your minister, or the prime minister, is just as risky as criticising your agency," the policies say.

"Equally, criticising your shadow minister, the leader of the Opposition, or the relevant spokesperson from minor parties, is also likely to raise concerns about your impartiality."

Rulebook 'fairly extraordinary': Union

Social media policies are commonplace in many workplaces, and generally prohibit workers from criticising their employer.

The guidelines state that public servants can partake in some political activities, such as sharing petitions, in the right circumstances.

But Community and Public Sector Union secretary Nadine Flood said they were a serious concern.

"If you email your mates something and they put it on social media, then your job might be under threat," she said.

"You name it, the Government does something on it — so what are public servants allowed to say? What's left?"

Ms Flood said while many private sector companies had social media policies, the Government's guidelines went too far.

"It is fairly extraordinary," she said.

Stephen Blanks from the New South Wales Council for Civil Liberties has warned the code of conduct could be constitutionally invalid.

"It's made under the Public Service Act, and therefore if it is an unreasonable restriction on people's right to engage in political communication it will be invalid," he said.

"It just goes too far. Restricting the ability of public servants in their private lives to criticise the Prime Minister or Government ministers or even the Opposition is just too far."

Guidelines 'not more restrictive': Commission

The Public Service Commission has defended the policy, saying it is not more restrictive.

Commissioner John Lloyd said the changes were about making the policy clearer.

"It's very little change — just amplifying it, making it easier to understand. We were really keen that staff could follow it," Mr Lloyd said.

"We are just telling people to be careful about what they post and how they manage their social media."

Mr Lloyd said while public servants were encouraged to participate in political life, the right was not unlimited.

"People have that freedom of political communication, but when you work for the public service there are some constraints on it," he said.

The commission said the guidelines were developed in consultation with staff and the CPSU.