The city's Department of Buildings is putting the brakes on plans for a controversial skyscraper on the Upper West Side.

This comes after the department sided with a challenge put forward by opponents of the plan.

The proposal calls for a 668-foot-tall luxury condo building that would sit on an oddly-shaped zoning lot that was configured by buying up development rights from the nearby Lincoln Towers.

Opponents argue the proposal lacks sufficient open space under zoning rules for a building that large.

In its ruling, the DOB agreed with the open space claim, and is now telling the developer to go back to the drawing board and show that the zoning lot it has assembled allows for the proposed building.

Opponents of the project are pleased with the ruling.

"The Department of Buildings is basically saying we don't see how the math adds up when you look at your open space and then use that open space to build something that's twice as tall as the buildings around it," said City Councilwoman Helen Rosenthal of Manhattan.

A spokesperson for the developer says the proposal conforms to all zoning regulations.