Australia’s Fair Work Commission has been asked to consider whether a retweet equals an endorsement, in a motion that accuses the commission’s own senior deputy president of bias.

In March 2016, senior deputy president Jonathan Hamberger retweeted a tweet from Liberal minister Michaelia Cash that criticised the Construction, Forestry, Maritime, Mining and Energy Union (CFMEU).

Labor gets millions in donations from the CFMEU. That's why they're against restoring the ABCC. Bring back the #ABCC pic.twitter.com/42Bn6di0TR — Michaelia Cash (@SenatorCash) March 17, 2016

The CFMEU has requested that Hamberger recuse himself from judging one of its applications to enter a work site, arguing that in the mind of a reasonable person, the retweet would create the impression he was biased against the union.

In a hearing on 4 October the union said a retweet was “commonly understood” to adopt or share the sentiments of the original tweeter.

“One of the issues that doesn’t seem to have been considered by any authority as yet, no doubt one day it will be, is what one takes from the concept of a tweet,” said the CFMEU’s barrister, Robert Reitano.

“By retweeting, can it be presumed that the retweeter adopts or shares the sentiments of the tweet? We’ve dealt with that in the written submissions and we’ve said that that is the position we take. That is the common understanding of what that means.”

During the hearing, the commissioner and barrister also discussed the mechanics of retweeting.

“In order for a retweet to occur – and I am not a Twitter person so I don’t know about this – you need to do two things,” said Reitano. “It’s not just a question of pressing a button. You need to press a button twice.”

Hamberger replied: “I can’t remember if that’s true but at any rate, yes.”

The deputy president has served on the Fair Work Commission since 2004, and created his twitter account (@JonathanHamberg) in August 2013. He has only tweeted 35 times in five years – including retweets.

At the time of publication, the most recent tweet on Hamberger’s account was about a workshop on workplace dispute resolution, and his most recent like was the trailer for the 2017 film Justice League.

Hamberger has since undone his retweet, but the original tweet from Cash is still available online.

It quoted a headline that said “CFMEU notches up 100 members before court”, and described this as a “century of shame” above a photoshopped image of Shorten with a cricket bat and helmet.

In a written caption, Cash criticised the CFMEU’s donations to the Labor party.

“Labor gets millions in donations from the CFMEU,” she wrote. “That’s why they’re against restoring the ABCC [Australian Building and Construction Commission].”

At the hearing, Reitano argued this represented a “condemnation of the CFMEU,” due to the prominence of the word “shame”.

Hamberger has reserved his decision and will rule on the case later.

Many Twitter users explicitly say that their “retweets do not equal endorsements” in their bios, but lawyers have not always recognised the sanctity of the phrase.

In 2017, the US Office of Special Counsel warned the then-ambassador to the UN, Nikki Haley, that her retweet of a Trump tweet endorsing a congressional candidate could count as an endorsement of that candidate.

The counsel warned this could potentially be a violation of the Hatch Act, which prohibits government workers from using their office to influence the result of an election (the president is exempt).

Buzzfeed traced the origins of the phrase “retweets do not equal endorsement” to Patrick LaForge, an editor at the New York Times, who claims to have started using it in 2007 or 2008.