Premier Gladys Berejiklian personally called the Catholic Archbishop of Sydney while he was in Rome to allay fears that NSW would block a $4.5 billion federal funding deal for schools.

Ms Berejiklian made the call to Archbishop Anthony Fisher last week as Catholic schools in NSW warn of a "catastrophic outcome" if their schools miss out or have to wait for federal funding.

The Premier's intervention comes as Catholic schools threaten to make funding a state election issue after Education Minister Rob Stokes said he would not sign a deal that "played favourites".

The Morrison government reignited the funding wars last month when it announced a $4.6 billion funding package for the non-government sector to ease its transition to a formula that would distribute money according to need.