BERKELEY, Calif. — Plenty of communities have resisted the U.S. Postal Service's sweeping real estate sell-off, battling to keep open historic buildings that speak of bygone civic grandeur and to guarantee old-fashioned mail service for the public.

Few have succeeded.

But this is Berkeley, home of the Free Speech Movement and protracted protests over civil rights, Vietnam and more. So when the postal service announced plans to sell Berkeley's 1914 Second Renaissance Revival-style main post office, decorated in New Deal-era art and situated in the heart of the liberal city's Civic Center, the town rose up.

Opponents staged a 33-day encampment on its steps, and the mayor and entire City Council joined forces to block the sale, with backing from U.S. Rep. Barbara Lee (D-Oakland) and state legislators.

Now, as CBRE — the private entity that holds an exclusive contract to broker postal service real estate — pursues a call for bids, Berkeley leaders have played a new hand that could set a precedent for other communities. They are racing to impose a zoning overlay for the entire Civic Center district that would force any buyer to put the buildings there to public use, and largely block any profit-making endeavors.

Meanwhile, the council has voted unanimously to sue if a sale goes through.

"They didn't really understand that we're just not going gently into the night," said Mayor Tom Bates. "People here are used to fighting for things they believe in."

For Berkeleyites, the issues resonate: Loss of the public commons, a blow to the nation's largest unionized workforce (40% of whom are minorities), with profits flowing to "the 1%."

"This is a cynical attempt to strip public assets from communities for private gain," Harvey Smith, an advisor to the UC Berkeley-based Living New Deal Project, recently told a packed Planning Commission meeting. "It's a heist of our cultural heritage."

The U.S. Postal Service has faced steep financial losses in recent years, due in significant part to a requirement imposed by Congress in 2006 that it prepay retiree healthcare obligations 75 years in advance.

Proposed legislation would repeal that requirement. But the postal service has held firm to a commitment to rid itself of underused and often aging real estate. Dozens of properties have sold over the last three years and 40 buildings nationwide are currently listed, Berkeley's among them.

What the postal service probably had not bargained for, however, was a Berkeley-style offensive.

Riling many here is the exclusive deal with CBRE Group, whose chairman, Richard Blum, is married to U.S. Sen. Dianne Feinstein (D-Calif.).

A recent e-book by investigative journalist Peter Byrne details allegations of below-market sales to CBRE clients and investors. (CBRE has declined to comment on those claims.) A June audit by the Office of Inspector General raised unrelated "conflict of interest" concerns and noted "poor oversight" of the CBRE contract.

Protesters began amassing in mid-2012 when the Italianate downtown post office made a list of buildings targeted for possible sale.

David Welsh, 78, a postal employee for a quarter of a century and union leader with the National Assn. of Letter Carriers, was among the first to fight. He demonstrated outside Blum's San Francisco office, took to Berkeley's streets with a megaphone and last summer pushed for a more visible presence.

As a result, about a dozen tents flanked the post office for 33 nights. Volunteers delivered home-cooked meals. Musicians performed on the steps. And weekly movies played on a portable screen. (Among them: "The Postman," a post-apocalyptic thriller in which a letter carrier saves the nation.)

Other residents packed public meetings. Among them was Moni T. Law, whose college-educated parents could not find employment in their native Alabama but like many African Americans climbed their way into the middle class as letter carriers in Los Angeles before launching other careers.

"It's constitutionally required that we have a U.S. Postal Service," Law, 53, who has fought the sale, said on a recent visit to the historic lobby. "It's not a nicety."

The City Council unanimously voted first to oppose the sale, and then to seek a one-year delay from the USPS in order to negotiate a compromise. (That bid was unsuccessful.)