Optus is set to face the federal court over a cross-selling campaign allegedly used to try to rush 138,988 mobile customers into churning their fixed-line NBN services across to Optus.

The Australian Competition and Consumer Commission (ACCC) claimed Optus had “misled consumers” by creating a false sense of urgency to encourage a switch.

“On 24 May 2018, Optus sent an email offering its NBN broadband services to 138,988 of its mobile customers, and advising them that their broadband service would be ‘disconnected very soon’ and encouraging them to ‘make the switch, before it's too late’,” the ACCC alleged.

“The ACCC alleges this was a false or misleading claim because, when the email was sent, Optus understood the recipients of the email were already being supplied with NBN-based services by a company other than Optus, and Optus did not have any reasonable basis for asserting they would be disconnected.”

The email was allegedly sent just two days after Optus was fined $1.5 million by the federal court for trying to force customers off its HFC network and onto the NBN in a bid to fast-track migration payments from NBN Co.

Optus vice president of regulatory and public affairs Andrew Sheridan said the telco "acknowledges the ACCC’s action today and its mistake."

"Optus has apologised to customers who received the mistaken communication and offered a costless exit for those who took out the offer," Sheridan said.

However, ACCC Commissioner Sarah Court said the ACCC "has had to take action about Optus’ advertising on several previous occasions, and it is concerning that we are again having to take them to court for alleged misleading statements about this issue."

“We are keeping a close eye on this sector and we will continue to take enforcement action where appropriate," she said.

The ACCC said it is “seeking declarations, injunctions, pecuniary penalties, compliance orders and costs” to be awarded by the court in this latest action.

In March 2012, the federal court ordered Optus to pay $3.6 million in penalties in relation to broadband advertising of its broadband plans.