Thousands of Catholic school teachers and support staff from about 350 schools will strike on Monday, protesting the Catholic schools employment body's attempt to pass an enterprise agreement without the union's endorsement.
This is the second time NSW and ACT Catholic staff have gone on strike since the previous enterprise agreement expired last December.
About 3000 teachers and support staff walked off the job in October after a Fair Work Commission decision changed the interpretation of the agreement's arbitration clause, saying that the wording suggests that, unless both parties agree, they will have no power to step in.
Independent Education Union NSW & ACT branch secretary, John Quessy, said this clause is a "detrimental thing for any worker".
"If you take the third party away, it takes the desire to resolve an industrial disputation away, as the other side knows that they can drag on the matter without it going to the Fair Work umpire," Mr Quessy said.
Staff from 100 more schools will join rallies throughout Sydney, Broken Bay, Parramatta, Armidale, Bathurst, Canberra, Lismore, Newcastle, Wagga Wagga, Wollongong.
Mr Quessy acknowledged the strikes will be disruptive for schools.
"Whether it's at the start of the year, end, during exam times, I don't think there is ever a good time to go on strike. Our members are aware this is disrupting and do this as a last resort. We have spent 12 months talking this [enterprise agreement] through," Mr Quessy said.
But Tony Farley, executive director of the Catholic Commission for Employment Relations, says the union is using "a misleading scare campaign to round up support after the majority of staff chose not to rally behind it".
"The disputes resolution clause that has the union hyperventilating is the exact same one school staff have now. The exact same one they've had for the past seven years. And it operates the exact same way to a clause the IEU approved only a matter of months ago for 450 private schools," Mr Farley said.
"To turn around now and say it's good for private schools but bad for Catholic ones reeks of confusion or hypocrisy - or both."