En Vogue -- Ex Label Honcho Sues ... Hold On, Ladies! Your Failed Comeback Cost Me Millions

En Vogue cheated on their record label and cost them over $100M ... so says the company suing the group for leaving them high and dry for another label.

According to the legal docs ... Rufftown Entertainment owner Rene Moore says he doled out $190K to front a huge En Vogue comeback in 2010 with OG members Cindy Herron, Terry Ellis and Maxine Jones that never happened.

TMZ even found video of them in the studio in 2011 excitedly laying down tracks ... but cut to 4 years later ... Moore says they never toured or cut an album and signed with another label -- Pyramid Records -- in 2014.

He believes they've cost him a fortune and wants both the group and Pyramid to cough up any potential money they cost him -- to the tune of well over $100 million.

Like they've sang, it ain't over 'til the fat lady sings.