UNION CITY -- City residents in November will decide whether to put houses, stores and elder-care facilities on a portion of land in protected hillside open space.

The City Council on Tuesday put an initiative on the November ballot asking voters whether 63 acres of protected land should be developed.

If voters agree, the Union City Flatlands Initiative would allow the Masonic Home of Union City to build affordable senior homes, low-density housing, retail space and elder-care facilities near the Hayward border.

The project would be built below the Masonic Home, a 116-year-old care center for about 270 senior citizens above Mission Boulevard.

"We've got an aging baby boomer community that absolutely needs senior services, and we can provide those services," said Gary Charland, executive vice president of Masonic Homes of California, owner of the Union City facility.

The development will create about 50 jobs in fields ranging from health care to maintenance to food services, Charland said.

"We think this is an exciting opportunity for the community," he said.

Even before Masonic Home leaders last month submitted about 5,000 signatures in support of the initiative, vocal opponents emerged, suggesting that it will be one of the fall election's more hotly contested issues.

Members of Save Our Hills, a Tri-City-area group working to spare the hills from development, say they oppose the plan. That's because the property is part of 6,100 acres protected by Union City's Hillside Area Plan and Measure II -- known as the Hillside Protection Measure -- both of which were approved in the mid-1990s.

As an alternative to putting the initiative on the ballot, the City Council on Tuesday could have opted to make it law, City Manager Larry Cheeves said.

Save Our Hills members, such as Rebecca Spindler, gathered outside of City Hall before the meeting Tuesday.

"This is this area's last pristine view of the hills," Spindler said, noting that the land has been protected for 20 years. "It seems we have to fight this over and over again. How many times does the public have to say no?"

The development would be built near the Hayward Fault, leading opponents to claim the housing units would be unsafe for its residents.

However, state law requires that any construction at the site would be subject to the Bay Area's seismic codes, Charland said.

"There are very strict building codes regarding what can or cannot be built in a fault zone, and we'll have to comply with all of them," he said.

"The City Council did the right thing," Charland said. "Now it's up to Union City voters to decide."

Contact Chris De Benedetti at 510-353-7011. Follow him at Twitter.com/cdebenedetti.