The main public sector union said it held concerns the tough changes could limit staff to only being able to retweet their published works while making online debate with other researchers impossible.

It comes months after a researcher within the Department of Parliamentary Services - the agency in charge of Parliamentary operations - was sued for defamation over a number of social media posts accusing members of the public of being associated with the Chinese Communist Party.

The new policy, which was approved at the start of August by DPS secretary Rob Stefanic, prohibits staff from posting work-related content without the approval of a senior executive.

But a DPS spokesperson denied the new policy would stop its academic and research staff from engaging in online debates.

According to the new rules, all DPS employees, including contractors, students, graduates and work experience staff, will need to ensure each post upholds the "integrity and reputation of the DPS and the Australian Parliament".

"It is important that your online conduct does not have a negative impact on the reputation of DPS or the Australian Parliament," the new policy reads.

"You must not post any content on or using a personal social media account that relates to your work at DPS without prior approval from your relevant Senior Executive Service (SES).

"This includes Twitter accounts that are private and accessible only to people who follow you."

Any breaches of the new rules could result in a member of the Communications and Media team referring the posts for investigation and action.

The definition for social media is broad and includes social network sites, like Facebook, Twitter and Instagram, but also extends to Wikipedia, Whirlpool, Gumtree and online gaming, such as World of Warcraft.

Comments posted on news sites are also considered within the policy's scope.

Community and Public Sector Union national secretary Melissa Donnelly said the fresh rules were limiting staff's ability to do the work they are employed to do.

"The union is always concerned about restrictions on any public sector employee's ability to engage on social media and participate in democracy," she said.

"In this particular circumstance, we are concerned that the restrictions may actually make it harder for some DPS staff to do their jobs, for example library staff who would only allowed to re-tweet their own publications, and research staff who would be prevented from engaging online with other academic work."

A DPS spokesperson confirmed the policy update was spurred on by the High Court's judgments in the separate matters of Banerji and Voller.

But the timing was also in response to recent legal proceedings where the DPS was pursued for being liable for defamation over tweets made by a staff member against a member of the public.

The DPS denied the changes would stop academic freedom within its research branch.

"The DPS social media policy does not prohibit staff from engaging in debate on social media," the spokesperson said.

"DPS staff can engage with other academics and peers through social media to the extent that this is not in conflict with their work as a Parliamentary Service employee.

"The DPS social media policy simply requires staff to seek manager approval prior to positing material related to their work at DPS."

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In June last year, independent journalist Marcus Reubenstein commenced defamation and copyright infringement proceedings in the Federal Court of Australia against Parliamentary researcher Geoffrey Wade and the Commonwealth.

The move was sparked after Dr Wade claimed Mr Reubenstein's website was operated by the Chinese Communist Party - a claim he strongly denied.

The proceedings have since been discontinued after a settlement was reached.