MSS guards provide entry-point security at the Mobil Refinery in Altona.

Union sources say the guards are paid $16.12 an hour. Six months of negotiations with MSS authorities have yielded no resolution.

Australian Liquor, Hospitality and Miscellaneous Workers' Union security state secretary Jess Walsh said a strike planned for early next month could disrupt major defence contractors, public hospitals, universities and government offices.

"It's disgusting that these highly trained, experienced professionals who protect the well-being of all Victorians should be left to struggle through life on unliveable wages.

"When things go wrong, guards are the first on the scene to stop violence, to help people in distress, or to perform first aid.

"As the biggest contractor in the country, MSS has a duty to step up and join other industry leaders, ISS and Wilson, to build an industry where public and guard safety counts."

MSS Security general manager George Diamond did not return our calls.