Business owners who arrived at the Mission Language and Vocational School Thursday evening to attend a social event organized by the developer of 1979 Mission St. were met by a group of about 30 chanting protesters who reiterated demands that the site be dedicated to affordable housing.

“No more monster in the Mission,” sang the protesters from the Plaza 16 Coalition, referring to the nickname activists long ago gave the project that promises to bring 331 units to 16th and Mission streets. At present, 41 of those are slated for affordable housing, with an additional 49 units to be built at a different site later. The developer, Maximus, is also considering setting aside some units for teachers.

Supporters of the project and members of the developer’s advocacy group, Mission for All, wore stickers with the text, “I am not a monster.”

Reporters were barred from attending the event, and it’s unclear which businesses attended. One nearby business group, the Valencia Corridor Merchants Association, has decided to remain neutral on the project, while Mission Merchant Association President Phil Lesser has voiced his enthusiastic support.

Four police officers guarded the Florida Street entrance to the building as protesters chanted and sang on the sidewalk, carrying signs that read, “We don’t negotiate with economic terrorists,” and “Monstruo fuera de mi comunidad” (“Monster out of my community”).

Joe Arellano, a spokesperson for the developer Maximus, said Mission for All advocates and staff had been gathering the support of thousands of people who have signed a petition backing the project.

At the business social, he said, Mission for All hoped to begin a conversation with merchants about their input, as well as some of the proposed changes to the project — like a market space on the plaza, and designating some units for teacher housing.

“We want to work with the city to find a solution for the community that works,” he said. “We recognize it’s a need here in the city.”

Because the building would be constructed directly adjacent to Marshall Elementary School (long a point of contention for opponents, who dislike the idea of a tall building casting a shadow over the school), Arellano said teacher housing would make sense.

Though merchants who attended the social declined to comment, one business owner at the protest opposed the project.

“Where are our workers going to live without affordable housing?” said Amparo Vigil, whose family operates Puerto Alegre. “If we don’t have workers who have a place to live, then we don’t have a business. Puerto Alegre disappears.”

Plaza 16 has long held that the project would send a shockwave of gentrification through the already increasingly unaffordable immediate vicinity. The increase in nearby property values brought on by the development, said Marilyn Duran of the group PODER, would incentivize landlords to evict long-term tenants paying low rents in favor of higher-income tenants attracted to the newly “cleaned up” area.

“I’ve been doing this since high school,” said Duran (now 27). “I haven’t seen less evictions because of market-rate development.”

As for the demands of the Plaza 16 coalition, which organized the protest and has long demanded that any development at 16th and Mission be entirely below-market-rate, Arellano said, “We want to talk to the community that is interested in meaningful dialogue. The people here have made their demands clear.”

The Planning Commission is expected to consider the project later this year, though no hearing date has been set.