The industrial umpire will rule on the fairness of a workplace ballot that saw the Turnbull government escape political humiliation at the hands of its own staffers by the narrowest of margins last month.
The United Service Union has cried foul over the conduct of the ballot of nearly 2000 workers in the office of federal politicians, alleging that many were unfairly denied the right to vote.
The office staff of MPs and senators voted to accept a new pay and conditions deal, offered under the Coalition's hardline public sector bargaining policy, by just 15 votes or 0.53 per cent.
The close vote indicates that large numbers of Liberal and National staff were prepared to risk political embarrassment to their bosses and vote against an agreement developed under the Coalition's hardline public sector industrial policy.
But the union has told the Fair Work Commission that the result should be thrown out and the ballot run again, saying it was unfair to stage the vote on the first week of the last sitting period of the Parliamentary year, an extremely busy time for staffers.
The union says the timing of the vote and the exclusion of as many as 540 staffers, many of whom were casuals who were only told late in the process that they were entitled to participate, definitely influenced the outcome of the ballot.
The challenge is believed to be the first of its kind in the present round of public sector bargaining, which has seen more than 150 workplace ballots held.
The Community and Public Sector Union has also lodged an objection to the agreement, raising similar concerns with the ballot process and also a potential issue with the agreement passing the test that workers should be Better Off Overall (the BOOT test).
"While the legislative bar for employer conduct of agreement ballots is quite low, there are genuine concerns from a number of staffers about this ballot," the union's national secretary Nadine Flood said.
USU general secretary Graeme Kelly said 539 eligible employees did not cast a ballot, with many of these people reporting that technical issues prevented them from voting.
"Following this ballot, the union was inundated with reports from parliamentary staff that they had either not received ballot papers or had not had access to a second payroll number required for the electronic voting process, denying them a say on their future pay and conditions," Mr Kelly said.
Meantime, bosses at Centrelink, Medicare and the Child Support Agency were warning of the effects on Friday of another strike by public servants working at the agencies.
Hank Jongen, chief spokesman with the agencies' parent department, Human Services, asked people to defer non-urgent business and use online and other self-service options.
"We expect the greatest impact will be in our service centres on both afternoons," Mr Jongen said.
"There may be reduced numbers of staff providing Centrelink and Medicare face-to-face services across the nation."
Human Services is also being challenged in the Fair Work Commission over its conduct during the three-year dispute with its workforce, with DHS's main workplace union, the CPSU, alleging the department has failed to bargain in good faith.
But Mr Jongen re-iterated the department's denials on Friday and blamed the union for the strike action, alleging that workers were being "forced" to take unpaid leave.
"Like the union, we want our staff to get a pay rise and we remain committed to bargaining in good faith to achieve this outcome," he said.
"Unlike the union, we don't think taking industrial action that inconveniences our customers, some of the country's most vulnerable residents, and forces staff to take unpaid leave, is the answer."
