If it’s autumn, it must be time for Airbnb ad wars in San Francisco.

Share Better SF, a coalition of housing activists, landlords, a hotel union and a hotel trade group opposed to vacation rentals in private homes, is launching a bus-shelter ad campaign on Thursday taking aim at Airbnb for suing its hometown and for not abiding by local laws.

“Dear Airbnb,” reads one of the Share Better ads. “You told us not to spend your tax payments ‘all in one place’ but now you’re making us spend taxpayers money on defending your frivolous lawsuit? Love, San Franciscans.”

Airbnb, a startup now valued at $30 billion, filed suit in federal court to block enforcement of an updated ordinance that would make it liable for heavy fines and criminal penalties for arranging short-term rentals in homes that have ignored the city’s registration requirement. The case will be heard in early October.

The Share Better ads are modeled after Airbnb’s “Dear San Francisco” Muni ad campaign last year that drew widespread scorn for its snarky tone of patting itself on the back for remitting taxes.

“We’re trying to encourage Airbnb to be a good citizen,” said Janan New, executive director of the San Francisco Apartment Association, which represents landlords. “We want to make sure that the public is aware of the ongoing issues. We did our part in negotiating legislation and attempting to uphold the law, and we’re asking that Airbnb do the same.”

Airbnb launched its own San Francisco ad campaign on Wednesday. The company plans to spend close to $1 million on a blizzard of spots on radio and TV that profile hosts and the ways the service benefits them. Share Better’s budget is a modest $51,000, largely paid for by hotel worker unions and a national hotel trade group, New said.

Airbnb called the bus-shelter ads “petty and misleading,” and said it wants to work with Share Better and the city to revamp the current registration system, which it characterizes as broken.

Only about 1,700 San Francisco hosts out of an estimated 10,000 have complied with a requirement to register their properties that took effect in February 2015. On Wednesday, The Chronicle reported that the registration fee could increase from $50 every two years to $250, because of a mandate that the short-term rental office cover its budget from fees and penalties. In essence, the fact that many hosts have refused to register is hurting the law-abiding ones who must pick up the slack.

Last year at this time, San Franciscans were deluged with far more Airbnb ads, as the company spent some $8 million to defeat Proposition F, a ballot initiative that would have curbed its business. Opponents spent less than $500,000.

Carolyn Said is a San Francisco Chronicle staff writer. Email: csaid@sfchronicle.com Twitter: @csaid