A taxpayer-funded pay rise 65 per cent higher than what public servants are entitled to has not been enough to tempt Serco workers at privately run Acacia Prison to agree to a new pay deal.
Guards at the prison, the scene of an escape this week, want Serco to consult them on staffing as part of an enterprise bargaining agreement to replace one that expired in late June, but the company is baulking.
The State's pay parity policy means private officers must be paid at least the same as Department of Corrective Services guards.
Almost $5 million of public money has been given to Serco under the policy since 2006, including $512,000 budgeted for this financial year.
It means that Serco guards must get a pay rise of at least 4.25 per cent a year in line with the 12.75 per cent over three years won by public officers last year, before the Government's tough new inflation-only wages policy came into effect.
Serco has offered 4.5 per cent a year for guards and 3.12 per cent a year for non-custodial staff.
A vote is due on Thursday.
WA Prison Officers Union secretary John Welch said workers wanted Serco to "consult, nothing more, over staffing levels" but the company had refused.
A Serco spokesman said the proposed clause would let the union determine staffing levels.