A massive public service strike has been confirmed.

The PSA says its attempts to broker a solution to next month's industrial dispute have failed, and more than 4000 members will walk off the job next month.

Advocates attended eleventh-hour meetings today at Inland Revenue and the Ministry of Business, Innovation and Employment - and say they were surprised at the employers' inflexibility.

National secretary Erin Polaczuk says bargaining teams were shocked and deeply disappointed at the employers' defiant take-it-or-leave-it attitude.

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She says for union members striking is a last resort.

She says both these disputes can be resolved if employers will come back to the table ready to seriously consider the PSA's offers.