CBS Emergency -- Suspicious Package Targeted Bristol Palin

Someone has it out for Bristol Palin on "Dancing with the Stars" -- TMZ has learned, the suspicious package that was sent to the CBS lot yesterday came with ONE demand ... remove Bristol from the show ... or else.

Sources at CBS tell TMZ, a note was attached to the white-powdery package that read something like, "This is what will happen to you if Bristol Palin stays on [the show]."

The white powder was later determined to be harmless -- but we're told law enforcement is still treating the situation as a credible threat, and is currently investigating the situation.

FYI -- this is the SECOND time Bristol has been targeted by a suspicious letter while appearing on "Dancing with the Stars." The first package was sent when Bristol first appeared on the show in 2010. It also contained a threat.