Unnamed Twitter employees told Forbes that an estimated four to eight bedrooms per floor were installed in the 1355 Market St. building. The Chronicle was unable to independently verify the claims. City records show that there have been no applications to convert any of portion of the building to residential use.

Twitter owner Elon Musk appeared to confirm that the company had installed beds and criticized Mayor London Breed for scrutinizing the company rather than focusing on the city’s drug crisis.

“So city of SF attacks companies providing beds for tired employees instead of making sure kids are safe from fentanyl. Where are your priorities @LondonBreed!?” Musk posted on Twitter, linking to a Chronicle story on the reported fentanyl overdose of a 10-month-old baby.

The city’s Department of Building Inspection is seeking to conduct a site inspection for potential violations and has reached out to the building manager for more information.

“We investigate all complaints. We need to make sure the building is being used as intended. There are different building code requirements for residential buildings, including those being used for short-term stays. These codes make sure people are using spaces safely,” said Patrick Hannan, spokesperson for the Department of Building Inspection.

If building code violations are found, the agency would issue a public notice of violation.

In the wake of Musk’s purchase of Twitter, some workers said publicly that they slept in the office amid high work demands.

Last month, Esther Crawford, Twitter’s director of product management, was photographed in a sleeping bag and wearing an eye mask in what appeared to be a conference room.

“When your team is pushing round the clock to make deadlines sometimes you #SleepWhereYouWork,” she wrote in a tweet, playing on the hashtag #LoveWhereYouWork.

Musk himself posted in a now deleted tweet that he would be working and sleeping in the headquarters “until the org is fixed.”

Twitter, which has laid off its communications team, didn’t immediately respond to a request for comment.

Shorenstein, which owns 1355 Market St. with JPMorgan Chase, declined to comment.

Twitter’s 2011 lease agreement with a Shorenstein entity, which was filed with the Securities and Exchange Commission, states that the landlord “may reasonably withhold its consent” to Twitter seeking to sublease its space to a “facility for the provision of social, welfare or clinical health services or sleeping accommodations (whether temporary, daytime or overnight).” The lease does not appear to state whether Twitter could operate sleeping accommodations itself.

The 1355 Market St. building is in a Downtown General Commercial zoning district, which allows for high-density offices, hotels, entertainment and residential uses.

In April, Musk tweeted a now deleted poll titled “Convert Twitter SF HQ to homeless shelter since no one shows up anyway,” in what appeared to be a criticism of the company’s remote work policy, which he later scrapped. Dan Sider, the city Planning Department’s chief of staff, told Bloomberg CityLab at the time that “from a regulatory perspective, converting this building into a homeless shelter would be fairly straightforward.”

Separately, the California Labor Federation said on Tuesday that Twitter terminated a contract with union janitors a day after they held a strike and picket line outside of the headquarters. Laid off Twitter employees are also seeking arbitration over claims that the company did not deliver promised severance packages and give legally required layoff notices.

Roland Li is a San Francisco Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf