The Fair Work Commission has labelled a bid by gas giant Woodside to access private emails of offshore workers a speculative fishing expedition based on an unfounded allegation that a union misled its members.

Woodside wanted to read emails from the Offshore Alliance to workers on Woodside’s gas platforms who were voting on whether to back the union to negotiate an enterprise agreement for them.

A Woodside spokeswoman said it wanted to be sure its employees wanted the union to act for them.

“That’s why we are taking the actions we are in the Fair Work Commission to ensure the process is thorough and robust and the legal requirements for bargaining have been met,” she said.

However, on Friday a full bench of the industrial court rejected an appeal by Woodside against a July ruling by deputy president Melanie Binet that said it was the commission, not the employer, that had to be satisfied that most workers favoured bargaining.

Offshore Alliance spokesman and AWU national secretary Daniel Walton said he was not surprised by the decision.

“But I am surprised that Woodside would be so persistent with such a hostile and odd tactic,” he said.

”Seeking access to employees’ private communications with their union is the kind of suggestion that’s strange when raised informally during negotiations, but to actually pursue it through the Fair Work Commission is quite bizarre.”

While Woodside’s request was only for emails from the union it is understood that email chains that included workers’ responses to the union could have been caught in the net.