About 120 V/Line guards were receiving eight per cent below the award rate despite working difficult hours in potentially dangerous situations, United Workers Union's Nicholas Richardson said.
The workers, who are employed to work for V/Line by contractor Corsec, will rally against the alleged wage theft at Melbourne's Southern Cross Station on Friday.
"They're sick of receiving less than the minimum wage and especially on a government contract," Mr Richardson told AAP.
"They take responsibility for guarding passengers on those late night routes. They're there because it's dangerous. They're there to protect passengers.
"They themselves need V/Line to protect them from a contractor that's seeking to profiteer from them."
Mr Richardson said the workers should be receiving six per cent above the award rate, in line with the state government's commitment to pay its guards the safeguard rate.
The union has contacted V/Line about the allegations but is yet to receive a response.
"We're taking this protest action, given the history of cleaners and guards being disrespected at V/Line," Mr Richardson said.
"We're wanting to see immediate and swift action to ensure that workers doing dangerous and difficult jobs are paid fairly."
Workers were prepared to keep rallying until their concerns were addressed, Mr Richardson said.
V/Line and Corsec have been contacted for comment.
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