Liberal Senator Zed Seselja says the main public service union has threatened jobs at the Australian Electoral Commission by not using it to run a protected action ballot.
But the Community and Public Sector Union says the senator should check his facts because the commission could not run the electronic ballot the union required.
The union has successfully applied to the Fair Work Commission for a private sector company to conduct its ballot for protected action at the Department of Human Services.
At the same time the CPSU has been critical of moves at DHS to outsource $30 billion of payments processing by saying it threatened public service jobs.
"The CPSU has criticised DHS' outsourcing of call centre work, document storage and payments, alleging it threatens the jobs of APS employees," Senator Seselja said.
"Based on this premise the CPSU's nomination of Queensland based RMK Investments Pty Ltd, trading as the Australian Election Company, to conduct the protected action ballot of DHS employees, equally threatens the jobs of Australian Electoral Commission employees.
"The CPSU has even gone so far as to pay to avoid using the AEC, since applicants for a protected action ballot pay the full cost of holding the ballot if they don't use the AEC.
"The CPSU and Labor have targeted DHS employees with baseless scares about superannuation, casual employees, call centres, documents storage and Medicare IT systems.
"Now the CPSU's double standards have been exposed."
CPSU national secretary Nadine Flood said the AEC did not have the funding to run electronic ballots.
"We would have been happy for the AEC to run it but they told us that they didn't have the resources to do the job," she said.
"The only alternative was for an AEC-run postal ballot, which wasn't practical given DHS has 15,000 members spread across the country in more than 600 regional and rural locations.
"CPSU members take democracy seriously so we needed a system that enabled as many people as possible to vote, which is why we made this decision.
"If Zed's genuinely concerned for the AEC's important role, he could start by advocating for a budget increase for their work."