Katy Perry Sued -- Did She Steal 'Black Horse' From Christian Song & Make It Blasphemous?

Katy Perry blatantly stole a song from a Christian hip-hop singer and then tarnished it with witchcraft, paganism and black magic ... at least that's the claim in a new lawsuit.

According to the suit -- obtained by TMZ -- Perry's hit song "Dark Horse" is a rip-off of an award-winning Christian gospel song called "Joyful Noise" ... that was released 5 years before Perry's track.

The suit was filed by an artist known as Flame -- along with other singers. They say Perry not only hijacked their religious music ... she also destroyed their reputation in the Christian music world ... because they're now associated with the anti-Christian witchcraft and imagery that appears in the "Dark Horse" music video.

They're suing for damages ... and want Perry to stop using any form of their music ... stat.