Hertz is gouging tourists who drive its cars across the Golden Gate Bridge, the City of San Francisco said in a lawsuit filed Wednesday against the rental-car giant.

City Attorney Dennis Herrera is accusing Hertz Global Holdings Inc. HTZ, , which operates the Hertz, Dollar, Thrifty and Firefly brands, of deceiving customers into paying exorbitant fees when they cross Bay Area bridges.

While other bridges in the area have the option of cash-only lanes, the issue is particularly thorny when it comes to the Golden Gate Bridge, one of the country’s most iconic landmarks and a top tourist attraction. The bridge eliminated human toll-takers in 2013, relying instead on an electronic payment system. Hertz vehicles use Plate Pass, which automatically pays the toll electronically. But Herrera said the system unfairly charges a $4.95-a-day “convenience fee” that, once activated, keeps accumulating every day even if the car doesn’t cross the bridge again.

For example, a five-day rental with a single round trip across the Golden Gate Bridge would cost $32.25 under Hertz’s program, whereas the toll for a single trip ($7.50) plus the convenience fee for a single day should total just $12.45.

“These practices are not only unfair, they’re unlawful,” Herrera said in a statement. “I am not going sit back and allow one of the largest rental car companies on the planet to take advantage of a world-renowned San Francisco icon to rip off thousands of California visitors and residents.”

Rental-car drivers have been complaining about the high fees since the bridge’s automatic payment system went into effect almost four years ago.

The lawsuit says the Plate Pass system violates state law against fraudulent business practices and false advertising, and financial penalties could total in the millions of dollars.

While other car-rental companies also charge extra fees for toll-bridge crossings, Herrera claims Hertz’s system is the most onerous, and doesn’t clearly warn customers of the extra charges nor of the option to opt out and pay the bridge fare directly online or through a mobile app.

Hertz did not immediately respond for comment.