Melbourne commuters may enjoy a "free travel day" after members of the Rail, Tram and Bus Union (RTBU) employed by Metro Trains voted to take industrial action next week.

The union will hold a four-hour stoppage after a meeting next Wednesday, and ticket barriers will be left open while officers will not be checking tickets or issuing infringement notices.

It said the strike would take place during the off-peak period from 10:00am-2:00pm.

Premier Daniel Andrews said there was no need for industrial action but RTBU secretary Luba Grigorovitch said negotiations were now into their fifth month and the union had been left with "few options".

"Our members have had enough of waiting and have reluctantly decided that they have no choice but to take industrial action," Ms Grigorovitch said.

She said talks only began after the union took Metro to the Fair Work Commission.

"This industrial action is aimed at Metro's hip pocket, not the travelling public," Ms Grigorovitch said.

"Whenever we plan to take action that impacts on the travelling public, such as stop work meetings, we will also seek to to implement a free travel day."

In a statement, Metro said it was "continuing to work towards reaching an agreement" with the union.

"Today at the Fair Work Commission, initiated by Metro and attended by RTBU, it was agreed that both parties would meet again this Thursday to progress discussions with a focus on achieving a fair outcome," it said.

"Metro and the RTBU will report back into the Fair Work Commission [on] Thursday.

"Metro maintains the view that any industrial action is unnecessary and will do all that we can to avoid any disruption for our customers.

"At this stage, Metro has not been notified of any industrial action."

Ms Grigorovitch said under workplace laws Victorians would be given at least five days notice ahead of any action taken.

The union is seeking an 18 per cent pay rise over three years for members, with 6 per cent to be paid every year.

The protected industrial action covers almost 3,000 staff, including drivers, authorised officers, signallers, station officers and administration staff.

It would be Melbourne's first train strike since 1997.

Union, Metro urged to 'think of public transport users'

Daniel Bowen from the Public Transport Users Association said a strike could cost Metro millions of dollars.

"I think the proposed disruption of services will directly affect passengers," he said.

"That really has to be minimised and we'd hope that the union and Metro sort this out as quickly as possible."

Mr Andrews said Metro and the union should try to resolve their differences through talks.

"I would ask all parties to this enterprise bargain to think of public transport users, to think of the broader Victorian community and to sit down and work through these issues, calmly, in a rational way.

"I don't think there needs to be any sort of action and I would again appeal to everybody involved, to all the parties involved, to sit down and work through the issues.

"That's in best interests of everyone."

Ms Grigorovitch said union members wanted to send a clear message to Metro.

"They want an outcome from the bargaining process and they want it soon," she said.

"It's time Metro recognised the contribution our members make to the record profitability which Metro is enjoying."