Tram drivers are joining industrial action by Melbourne’s rail workers, threatening to throw the network in chaos.

Union members could hold a 24-hour work stoppage, which is likely to cause heavy disruptions on the city’s extensive tram system.

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The Rail, Tram and Bus Union voted for workplace stoppages of at least four hours and bans on overtime and uniforms as part of a four-month battle with Yarra Trams over a new industrial agreement.

On Monday, train staff announced they would enforce two “free travel days” as part of their industrial action against Metro.

Tram staff are pushing for a pay rise of 18 per cent over three years, rejecting an earlier offer of nine per cent by Yarra Trams.

– with AAP