Public sector workers from 21 federal government departments and agencies have vowed to continue a campaign of industrial action for better pay and wage conditions.

About 600 workers walked off the job for a rally in the Brisbane CBD on Wednesday afternoon.

They were from agencies including Medicare, Customs officers and CSIRO, with the crowd gathering at Roma Street's Emma Miller Place to criticise the Abbott government.

Community and Public Services Union president Alistair Waters said his union had been trying to negotiate a pay deal with the government for more than a year.

"They insist on putting offers on the table that cut wages and slash our members' rights and conditions. All this on top of 17,300 job cuts," he said.

Mr Waters said the government had made pay rise offers up to just 1.5 per cent, which is below the inflation rate.

He said the pay deal would affect about 250,000 workers and was creating an "enormous amount of uncertainty".

Customs staff were likely to strike on July 1, when their Enterprise Bargaining Agreement expires, Mr Waters said.

Department of Employment delegate Shaz Gerchow said 95 per cent of her department staff voted against a pay deal which she claimed would have resulted in pay cuts and longer hours.

She led the crowd in chants against proposed public service cuts.

Queensland Council of Unions secretary Ron Monaghan said state colleagues backed their federal counterparts.

"If the Abbott Government continues these attacks on you, they're laying the path to their own demise," he said.

Mr Monaghan referenced the LNP's Queensland election loss as an example of the voters rejecting public service job cuts.

Similar protected strike action is expected in Townsville on Thursday and Cairns on Friday.