Sydney commuters are facing more disruption just months after a deal was struck with heavy rail unions, but this time it is pay negotiations between metro workers and the network’s private operator that have broken down.

On Thursday the Fair Work Commission approved an application for a protected action ballot by Sydney Metro workers, who are represented by the Rail, Tram and Bus Union.

Members will now vote on whether to take action and what kind of action they can take.

The order, seen by Guardian Australia, shows they will vote on whether to authorise a series of measures similar to those taken by heavy rail workers during late 2024 and early 2025, which caused major disruptions and commuter delays.

Under the order, which members must vote on within 14 working days, actions could escalate if an agreement is still not reached.

They include taking an unlimited number of stoppages of work between a minute and 72 hours, smaller actions like wearing and distributing union material, and other “bans, limitations and restrictions”.

At the height of rail industrial action in February, 576 train drivers and guards failed to show up to work while others implemented “go-slow” actions, which saw trains running 23km/h slower than usual in areas where the speed limit is more than 80km/h.

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In July, heavy rail workers from unions including the RTBU and the Electrical Trades Union voted to accept a pay offer agreed in May.

At the time, the New South Wales transport minister, John Graham, said the agreement would provide relief from the disruption “that a million daily rail commuters have been forced to endure while just trying to get to work and get around”.

That deal, under which 13,000 rail workers receive a 12% pay increase over three years, plus back pay, kicked in last month.

During the industrial action, metro services were unaffected, with many commuters favouring the high-speed network amid heavy rail delays.

Sydney Metro trains are driverless, although customer service attendants work inside the trains and on station platforms.

The bargaining agreement with the RTBU and another union, Professionals Australia – which expired in August – covered these workers as well as signalling and control centre staff. Negotiations had stalled over safety measures. One of the RTBU’s demands is the installation of drivers’ cabins on metro trains.

A spokesperson for the RTBU’s NSW branch said no immediate action was planned, but safety remained the “top priority” in negotiations.

“This application for a protected industrial action ballot is simply the next step in ensuring Metro workers get the fair wages and conditions they deserve,” they said.

“The Metro system has been heralded as a great success in Sydney, but we’ve got to remember that its success rests entirely on the shoulders of the workers who keep it moving every day.”

Unlike rail workers, who are mostly employed by the government, metro workers are employed by the privately owned Metro Trains Sydney – majority-owned by the Hong Kong-based MTR Corporation – which operates the network in a partnership with the government-owned Sydney Metro.

The potential industrial action comes amid delays to the release of a key report into safety on the heavy rail network. The inquiry, headed by Kerry Schott, was commissioned after a high-voltage wire fell on the top of a train at Homebush in May, trapping 300 passengers and causing massive disruption.

The NSW premier, Chris Minns, said on Wednesday that the draft report was “sobering reading” and there were “comprehensive changes needed”, but would not say when it would be released.

A spokesperson for Metro Trains Sydney said the company continued to “engage with the Rail Tram and Bus Union and Professionals Australia to finalise the agreement”. The company had strategies in place in the event of industrial action.

Graham declined to comment.