SAN FRANCISCO (KCBS) – The debate over plans to build a 47-story condominium tower on Mission Street downtown has spilled north of Market Street to Union Square, where opponents have raised concerns the building will cast too much shadow over the plaza.

The mechanical penthouse atop 706 Mission Street has been modified enough to get the greenlight from both the City Planning Commission and the Recreation and Park Commission at a joint hearing Thursday.

Kevin Guy of the San Francisco Planning Department explained the approval by noting the shadow in Millennium Partners’ revised plan would fall briefly over just one corner of Union Square Park early in the morning before the crowds arrive, “during limited times of the year.”

But the 480-foot building will still need a special height exemption from the Board of Supervisors to proceed. Opponents such as Matthew Schoenberg believe the city should not be raising the so-called shadow limit on new high-rise buildings.

“There exists no feasibility study that is properly done that could in any way justify the continued erosion in our parks,” he testified.

Schoenberg was in the minority at the hearing, in part because the bottom four floors of this condo tower would house the Mexican Museum which has been housed in a much smaller temporary site at Fort Mason since 1982.

“It is time to have a permanent home for the Mexican Museum,” said Carlos Solórzano, CEO of the Hispanic Chamber of Commerce of San Francisco.

Dozens of museum supporters took to the microphone endorsing the development and urging the city to build something that would properly showcase the contributions and history of Latinos in the Bay Area.

Schoenberg insisted his objections have nothing to do with the museum. He said the city should enforce code restrictions uniformly rather than granting project by project exceptions under pressure from developers.

“We do want to support the Mexican museum. We do want to have this project, but we want to have our parks protected as well,” Schoenberg said.

(Copyright 2013 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)