A union-backed action against the Federal Government’s national workers’ compensation scheme could prevent private sector operators switching from state-run schemes.

Sydney-based carpenter Jason Cowie is seeking a court order preventing construction giant John Holland from moving to the federally administered Comcare.

If Mr Cowie can establish that he and other John Holland employees will be worse off with Comcare than under the NSW WorkCover system, it could prevent other private sector companies from going national.

The Construction, Forestry Mining and Energy Union, which is backing Mr Cowie’s action, says John Holland’s move could trigger a rush of construction companies into Comcare, in which premiums are cheaper and payouts are capped at a lower level than for state schemes.

Unions also have less influence with companies under Comcare. For example, instead of having an automatic right of entry to investigate workplace safety, unions must give 24 hours’ notice.

Companies appreciate working under the one system, rather than juggling several state schemes. Comcare now covers 18 companies.

John Holland, which is expected to save at least $8 million in premiums under Comcare, will contest the case in the Federal Court on August 6.