Melbourne's rail and tram networks must be returned to public hands so profits can be invested in improving infrastructure, the union movement has told Premier Daniel Andrews.

The Rail, Tram and Bus Union is leading a call for the Labor government to use the 2017 expiration of the contracts for Metro and Yarra Trams to allow the state to once again operate the networks.

Both companies have bids before the government and a decision on the next contract is expected soon.

RTBU secretary Luba Grigorovitch, writing in The Age, argues that profits are being wasted on propping up foreign companies when the cash would be better spent on improving Victoria's public transport infrastructure.