IRVINE

Irvine Unified trustees are expected to vote Tuesday to formally join cities and schools fighting the proposed airport at the former El Toro Marine Corps Air Station.

School board members said they became interested in joining the El Toro Reuse Planning Authority after its directors introduced a nonvoting, nonpaying affiliate membership two months ago; school districts are prohibited by state law from spending money on activities unrelated to education.

The new affiliate memberships allow organizations that could not pay to still show support for anti-airport activities, authority spokeswoman Meg Waters said.

The Saddleback Valley and Capistrano unified school districts already have voted to join the authority as affiliate members.