Which group scored a hit song with “Ladies’ Night”?

The late 1970s were a brutal time to be a funk band. Disco was dominating the airwaves, and if you couldn't make people dance to a four-on-the-floor beat, you might as well pack up your horns and go home. But one band took that criticism and turned it into their biggest mainstream breakthrough. Which group scored a 1979 R&B hit with "Ladies' Night"?