The last major planned tower in San Francisco’s Transbay district is caught in a fight over shadows, threatening a major new Salesforce office and funding for affordable housing.

The 806-foot proposed skyscraper at 546 Howard St. would be the city’s fourth tallest. Chinatown activists oppose the project, also known as Parcel F, because of shadows it would cast at Willie “Woo Woo” Wong Playground nearly a mile away — despite a city study that found the shadows fell within legal limits. The tower would cast a shadow from around 8 to 8:20 a.m. from November to late January, a study found.

Phil Chin, chairman of Committee for Better Parks and Recreation in Chinatown, rejected the conclusion that the shadows are legal in an October letter to the city, and said no new shadows are permitted. He cited in part a 1989 city memo, but city officials said the tower falls within guidelines set in 2012 that allow taller buildings in the Transbay district.

Willie “Woo Woo” Wong Playground, named for a 1940s basketball star and Chinatown native, is undergoing a $13.5 million renovation. It’s a crucial source of open space for low-income Chinatown families, Chin said.

“They need to get as much park space and sunlight as possible, so we oppose this project and we hope that you will force the proposer to reconsider and redesign,” Chin said at a Planning Commission hearing in October. He didn’t respond to a request for additional comment.

Eliminating the shadow completely isn’t possible, because it would require cutting 23 of the tower’s 62 floors, according to comments by C.J. Higley of Farella Braun + Martel, the project’s land use attorney, at a city hearing this month. “The reality is the site is incredibly constrained,” he said.

Parcel F, which includes offices, condos and a hotel, isn’t the first shadow fight in the area. Transbay project Oceanwide Center, which will include the city’s second-tallest tower and cast larger shadows, agreed in 2016 to pay $12 million for parks in Chinatown to compensate for its impact. In April, the city rejected a housing project in the South of Market area because it would cast shadows on Victoria Manalo Draves Park. A new Financial District tower at 350 Bush St. expanded Chinatown’s St. Mary’s Square to offset a new shadow.

Backlash against shadows stretches back to the voter-approved 1984 Proposition K, which blocks new buildings over 40 feet that cast adverse shadows on public parks, unless the Planning Commission decides they are insignificant.

“People have always used the shadow issue as a way of stopping or getting more concessions out of a project,” said Jeffrey Heller, president of Heller Manus Architects, which worked on 350 Bush St., Oceanwide Center with architect Foster + Partners, and designed another Transbay tower, 181 Fremont.

“In this environment right now, where there’s growing negativity, it creates a hurdle that can be too high for some projects and can in fact kill them,” he said.

Hines, Urban Pacific and Goldman Sachs are developing the Parcel F tower and meeting with Chinatown community groups, Higley said at the hearing.

“I’m happy to report those conversations have been amicable and very productive. We made great strides there,” Higley said.

The developers continue meeting with Chinatown groups to “address their concerns with the project and enhance our community benefits,” said Julie Chase, a spokeswoman for the developers. “We look forward to proceeding together to get the tower under way.”

Amid opposition, the Planning Commission delayed an October vote to begin Parcel F’s final approvals process. Commissioners said they generally support high density in the Transbay area but urged the developers to get Chinatown’s support. The Planning Commission advanced the project at a hearing last week, and a final vote is scheduled in January. Higley said the project is expected to win full support by January.

Salesforce, the city’s biggest private employer, leased all 325,000 square feet of office space in the Parcel F tower more than a year ago, with room for 1,500 employees. A Salesforce spokeswoman said the company’s plans have not changed.

The tower also calls for 165 condos and 189 hotel rooms, and would help fund 337 affordable apartments a few blocks to the east. Chin also criticized the affordable housing component, saying the maximum income limits are too high for Chinatown residents to benefit. Residents would be restricted to those with up to 40% of the area median income, or $49,250 for a four-person household.

Despite a prime location adjacent to the Transbay transit center, the Parcel F site faced a series of challenges. The Transbay Joint Powers Authority, the government entity that controls the site, planned to sell the land in an unprecedented live auction in September 2015. The auction was canceled the day before as the stock market tumbled.

Residential developer Crescent Heights later agreed to buy the site for $165 million, but pulled out because it wasn’t able to meet a 35% affordable housing goal.

The Hines team bought the site for $160 million in 2016. Next month’s vote will mark the project’s fourth year of city reviews.

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