Jessie J -- Accused of Jacking 'Domino' ... From a MAN

British pop star Jessie J is a "Domino" thief ... so says the singer of a California band ... who claims Jessie's smash hit is simply a ripoff of one of his songs.

Jessie is being sued by Will Loomis from the band "Loomis & The Lust" ... whose music has been featured on MTV's Iggy and the Spike TV show "Blue Mountain State."

In the docs, Loomis claims Jessie's 2011 hit "Domino" incorporates huge chunks of his 2008 song "Bright Red Chords."

Loomis claims he never gave Jessie permission to jack his song ... and is now suing for damages. So far, no comment from Jessie J's camp.

Fun Fact: Jessie J has sold more than 11 million singles and 2.5 million albums to date ... Loomis & The Lust have a very nice Myspace page.