BERKELEY — Making good on a months-long threat, the federal government has filed suit over the rezoning of the downtown post office, saying the city did it to prevent the U.S. Postal Service from selling the property.

City Attorney Zach Cowan said Monday he had no comment.

The postal service has contended for several years that the Berkeley Main Post Office, at 2000 Allston Way at the corner of Milvia Street, is underused. It first put the property on the market in 2013, but took it off again after an interested party, Berkeley-based developer Hudson McDonald, pulled out in late 2014.

In September 2014, the City Council established by ordinance the Civic Center District Overlay, which restricts the nine parcels that form the Civic Center Historic District to uses such as libraries, courts, museums, live performance theaters, schools and other public agencies, and other government, civic and nonprofit uses. New buildings and additions in the Civic Center District are restricted to a height of 50 feet.

In April, the U.S. Department of Justice wrote a letter to Berkeley protesting that the rezoning had “so drastically reduced the value of the property as to render a sale untenable.” The letter further contended that the city’s action violated the Supremacy Clause of the United States Constitution, and is pre-empted by the Postal Reorganization Act and the Constitution’s Postal Powers Clause.

The letter gave the city an ultimatum, May 20, to respond, and declared that the federal government would file an action “on or about May 27, 2016.” That deadline came and went.

In July, Cowan said the city had not filed a written a response but that he’d had “a number of conversations” with a U.S. attorney.

The suit, filed Monday in U.S. District Court, Northern District of California, contends that the Civic Center District Overlay was “enacted primarily to prevent the sale of the Berkeley Main Post Office” and that it “limits the property to civic or nonprofit uses.”

It asks the court to declare the overlay invalid and to permanently enjoin the city “from targeting the Berkeley Main Post Office through substantially similar ordinances designed to prevent the sale of the property.”

The federal government also is asking to be awarded its costs of the suit.

Contact Tom Lochner at 510-262-2760. Follow him at Twitter.com/tomlochner.