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 claimed.
The workers, who are employed to work for V/Line by contractor Corsec, rallied against the alleged wage theft at Melbourne's Southern Cross Station on Friday.
A group of about 30 loudly made their way through the station at lunchtime chanting and banging drums as passengers watched on.
"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."
Corsec has denied the allegations, saying they have no record of workers or the union coming forward with wage theft claims.
"All our staff are paid in total accordance with the Corsec Services' Enterprise Agreement (2023)," the company told AAP in a statement.
"If any of our staff are claiming underpayment or have issues of any type we would welcome their inquiries and we would endeavour to resolve any problem without hesitation."
Corsec said it was only made aware of the allegations when contacted by AAP.
"We extend a challenge to the UWU to present specifics of their allegations so that the authenticity of their claims can be examined," the company statement read.
Mr Richardson maintained 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."
One worker, who did not wish to be identified, said he had never been part of a protest before but felt compelled to march as he wanted better pay and conditions.
"It can be dangerous working the night shift with only one guard," he said.
"You never know what's going to happen."
Workers were prepared to keep rallying until their concerns were addressed, Mr Richardson said.
V/Line has been contacted for comment.
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