Electricians tasked with keeping the lights on at Parliament House have walked off the job arguing for better pay as the relevant department reviews staffing classifications as part of negotiations.
The Electrical Trades Union has set up a picket line outside the national institution for 24 hours, saying electricians working for the Department of Parliamentary Services were paid about $30,000 below the industry average.
The union will be joined by the Australian Manufacturing Workers' Union and CFMEU on the lawns of parliament on Monday for a rally as politicians gather in the nation's capital.
"The workers who keep the lights on at Parliament House are being blocked out when it comes to fair wages," the electrical union's NSW and ACT secretary Allen Hicks said.
Morale had hit rock bottom, Mr Hicks said.
"Because permanent trades staff's wages are so low, positions are left vacant, yet the department is willing to outsource the roles at a much higher rate of pay," he said.
"It's a kick in the guts to have contractor staff who are paid competitive industry rates working alongside trade-qualified permanent employees who are earning the equivalent of a contractor apprentice."
Workers had a right to protest and measures had been put in place to minimise disruption to the operation of Parliament House, the Department of Parliamentary Services said.
The department insisted it had negotiated in good faith on the proposed enterprise agreement.
"All claims and proposals were genuinely considered," it told AAP in a statement.
"As part of the bargaining negotiations, DPS has undertaken to conduct a review of the classification of staff in the affected areas."