A proposal that would hold home sharing platforms like Airbnb responsible for listing units not registered with the city moved one step closer to approval on Thursday when it secured a recommendation from a Board of Supervisors committee.

“This is not about changing the existing law. It’s simply about making sure that this law that has been in effect, that this law is actually enforced,” said Supervisor David Campos, one of the co-sponsors of the legislation. “It’s ultimately about corporate responsibility.”

Under a city law that went into effect in February 2015, residents renting their spare rooms through a home sharing platform like Airbnb must get a business license and registration number from the city, as well as pay hotel taxes.

Those hosts can face serious fines if the new Office of Short Term Rentals — a city enforcement body for homesharing — finds hosts who have not registered or are renting out a non-primary residence. More than 75 percent of short term rentals in the city unregistered with the city, according to estimates from a Budget and Legislative Analyst’s report.

The proposed legislation would fine home sharing platforms $1,000 a day per noncompliant listing, requiring companies like Airbnb to confirm the host’s registration number before allowing them to post a rental.

Critics of the existing law have said that it is unenforceable without a means for the city to know which units are being rented out on platforms like Airbnb, and say the penalty system shifts the enforcement burden from the city onto the home sharing platforms.

“The main thing this legislation does is hold platforms themselves accountable for registration, in the same way that Hertz is responsible for making sure that the cars it rents out are registered with the DMV,” said Charlie Goss of the San Francisco Apartment Association, a group that represents rental property owners.

But opponents of the new proposal said they worried it would put Airbnb and other platforms in an untenable position of having to police their own users, a responsibility that lies with local government. Some say that also opens the city up to lawsuits from platforms claiming that the city is trying to make them regulate user-produced content.

Jim Lazarus of the San Francisco Chamber of Commerce likened the proposal to restricting newspapers by requiring them to verify a company’s business license before accepting advertising.

“What you’ve heard today is a failure of enforcement by the city and that should not be put on the backs of independent companies that are located here and throughout the world.”

Making platforms specifically responsible for checking registrations was a recommendation of the Planning Commission when earlier legislation was being considered. Planning Commissioner Dennis Richards reiterated his support at Thursday’s board meeting.

“I drive around in my car with a license plate on it. It doesn’t tell people who I am or where I live,” said Richards. “Could you imagine if 75 percent of people didn’t drive around with license plates? It wouldn’t make any sense.”

Despite being aimed at platforms, not hosts, some said it created another obstacle for hosts trying to rent out their homes for extra income.

“Don’t just drop the hammer on people who are struggling to get registered,” said Laura Clark, president of pro-development group Grow SF. “This legislation doesn’t really solve that problem, this just adds another hammer to the problem.”

For individual homesharers, the primary concern on Thursday was a prohibitively cumbersome registration process, especially with the new requirement from the city that hosts turn in a list of all of the furniture and equipment in a rental unit, their value, and when they were acquired, for tax purposes.

“It’s also known that the process is very cumbersome. It takes up to three months or more to get registered,” said Doug Nielsen, a registered host. “The city must find a way to simplify this process.”

None of the hosts who commented on the legislation at the hearing said they were unregistered.

Alix Rosenthal, a vice chair of the San Francisco Democratic County Central Committee, agreed that commercial landlords using the platforms are a problem. Rosenthal herself is an Airbnb host — and a recipient of $2,500 in re-election campaign contributions from the company, and also raised concerns over the registration process.

“It was relatively onerous,” she said. “My experience is fairly common. Folks aren’t going to go through this process unless they’ve tried it. Requiring registration from day one will likely kill [short term rentals].”

Supervisors on the committee decided to recommend the legislation, however, citing concerns that hosts take rental housing off the long-term market and offer it up to the more lucrative short-term rental market, worsening the city’s housing crisis. The full Board of Supervisors is expected to consider the law on June 7.