Catholic schools are targeting One Nation and the Shooters, Fishers and Farmers Party as part of a concerted political campaign for more funding in the lead-up to the NSW election.

Citing their campaigning success at the federal level, Catholic school bosses have written to their 600 principals about their push for more money to spend on building and maintaining schools.

Catholic Schools NSW is pitching their case for funding to the major political parties ahead of next month's state election. Credit:Michele Mossop

Former NSW education minister Adrian Piccoli said the Catholic Church was being politically open.

"I never saw anything quite as overt as sending something like this out, listing marginal seats, talking about One Nation, sending letters to 600 principals," he said. "Catholic schools are an important part of the education sector, but they can't have undue influence."