An ACT Senator says the CPSU is hypocritically threatening the jobs of its own members, while claiming to fight on their behalf.

ACT Liberal senator Zed Seselja says the biggest union representing public servants is upholding a double standard, by outsourcing its protected action ballots to a third party, rather than running the votes with staff from the Australian Electoral Commission.

But the CPSU says with over 160,000 members, it needs to rely on electronic voting offered by groups other than the AEC to get quick results.

Senator Seselja says he can see no logistical or legislative reason why the AEC could not run the CPSU’s polls in the form of a postal ballot.

“The decision to outsource was a deliberate choice by the CPSU, which publicly suggested that the AEC couldn't do this [protected action ballot], because it was intent on conducting an electronic ballot,” he said after a Senate Estimates hearing on Tuesday night .

“The CPSU apparently did not even approach the AEC to conduct a recent [ballot] of Department of Veterans' Affairs employees.”

“The CPSU's hypocrisy and dissembling on outsourcing is now evident for all to see.

“Incredibly, it is using its own members' money to divert this work away from its members in the electoral commission to the private sector.

“It has criticised DHS' outsourcing of call centre work, document storage and payments, alleging it threatens the jobs of APS employees,” he said.

But CPSU national president Alistair Waters has told Fairfax Media that the senator should check his facts before taking cheap shots at the union.

“As we pointed out last year when he first made this slanderous claim, we had asked the AEC to run electronic ballots but it told us it didn't have the resources to do the job,” Mr Waters said.

“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.

“Employers can use emails to get staff to vote on agreements so we feel we should running ballots electronically because they are both efficient and timely.

“If Zed's genuinely concerned for the AEC's important role, he could start by advocating for a budget increase for their work including the capacity for them to run electronic ballots.

“Instead he would rather make mischief by repeating claims he knows are simply not true.

“If he is so concerned about the public sector, then perhaps he can stop his government from cutting a further 8,500 jobs from the public service.”