The Port of San Diego gained a new opponent to its plan to use a fee on rental cars to build a parking structure in Chula Vista: the San Diego International Airport.

The airport is joining a lawsuit against the Port filed by Enterprise Rent-A-Car Co. and Hertz Corporation in June challenging the $3.50 fee, which they allege is an unlawful tax that requires two-thirds voter approval. The airport and rental car companies are tenants of the Port of San Diego, a government agency that acts as landlord for businesses spanning five cities along San Diego Bay.

By joining the lawsuit, the airport seems to have instigated a dormant feud with Assemblywoman Lorena Gonzalez, who earlier this year proposed a bill that would have folded the airport into the Port, before softening the measure by ending the takeover bid and instead proposing a simple joint task force.

Gonzalez said she now plans to pull that softer bill and threatened to again propose a major overhaul next session.

In April, the Port reinstated the rental fee to bring in at least $5 million a year to pay for a $40 million parking structure planned as part of the 535-acre Chula Vista Bayfront development project. The fee would last until the structure is paid off, and was previously collected from 1999 to 2006 to fund a $29 million public parking structure near the San Diego Convention Center and Petco Park.

Airport spokeswoman Rebecca Bloomfield said in a statement the airport “does not object to the imposition of the fee on rental car transactions occurring off airport property. The Port’s fee on an on-airport transportation mode is unprecedented and should include input from the Airport Authority,” which was not sought before it was reinstated.

The move riled Port of San Diego leaders and others across the South Bay who say the lawsuit threatens to derail the long-sought Chula Vista project. The 1,600-car parking structure is supposed to be built alongside a new convention center, hotel, shopping center, restaurants, shoreline promenade, RV campground and 200 acres of parks and open space.

The Port contends the rental car charge is a fee permitted by law without voter approval.

Not so, says the car companies.

“The Charge is not a ‘User Fee’ benefitting the customers; instead, the Charge is for the benefit of the Port so that it can use the funds in the future to construct parking structures near a planned Chula Vista convention center. Given that the parking structure has not been built, none of the customers being assessed the Charge can ‘use’ the parking structure,” the lawsuit by the rental car companies says. Even when it is built, the lawsuit claims “only a miniscule percentage” of Enterprise and Hertz customers would use the parking structure 10 miles away.

“The overwhelming majority of cars that will use the convention center’s parking facilities will not be rental cars originating from car rental companies on Port Property,” the lawsuit says. “The Charge will thus primarily and overwhelmingly benefit the general public, not customers of car rental companies situated on Port Property, belying the Port’s designation of the Charge as a ‘User Fee.’”

Port leaders balked at the airport’s decision.

“If the Airport lawsuit succeeds, it would result in uncertainty and could delay plans for a 1,600-space parking garage, integral to success of the new convention center and related 1,600 hotel rooms,” Port Chairman Rafael Castellanos said in a statement. Castellanos also argued it’s a matter of equity for the South Bay, which has been overlooked for years as past projects benefitted other waterfront areas.

“Too often in the past desirable projects have benefited the central and north bay but offered little in the way of new jobs and economic growth in the south bay,” he said. Castellanos claimed there was “broad regional support” for the fee to fund the city of San Diego parking garage years ago, “But when we now work to expand the South Bay tourism economy, the Airport has initiated this short-sighted and hostile act that interferes with 20 years of hard work by the Port, the City of Chula Vista and leading environmental groups.”

Other South Bay leaders were incensed by the news.

Gonzalez reacted by announcing plans to pull her revised bill, which would have created a committee tasked with focusing on mobility issues around the airport comprised of Port and airport officials, and others.

But she appears to be reinvigorated toward larger changes. She tweeted Wednesday that it was a “slap in the face to my district” and pledged to “look at possible governance changes next year.”

Chula Vista Mayor Mary Salas called out the airport in a statement, noting it currently collects a higher rental car fee to finance its own parking structure.

“If rental car fees are appropriate for parking structures at the airport and the San Diego Convention Center, why are the fees inappropriate for a parking structure at the convention center on Chula Vista’s bayfront? The Airport Authority must drop this frivolous lawsuit and begin acting as the regional body it was intended to be.”

“I strongly urge the Airport Authority to reconsider this parochial and ill-advised course of action,” Chula Vista Councilman Stephen Padilla, who is also a California coastal commissioner, said in a statement.

The Chula Vista Bayfront project was approved by the California Coastal Commission in 2012.

The South County Economic Development Council also issued a statement criticizing the airport’s decision.

“We call on all parties involved in this issue to come to the table in good faith and resolve this without going through a lengthy court process, so we can continue moving this project forward,” the statement said.