Fantasia Barrino is under a self-imposed lockdown -- after the "American Idol" champ received a threatening letter.
It all started last night at the Pantages Theater in L.A. -- Fantasia was reading her fan mail after a performance of "The Color Purple."
Fantasia's manager tells us Barrino became alarmed over a disturbing letter loaded with racial slurs -- including the n-word -- and a line that read, "go back where you came from and die."
We're told the person who wrote the letter claims he used to work as a security guard for Fox while Fantasia was on "A.I."
Fantasia's manager tells us the singer immediately contacted theater security -- which then contacted the LAPD.
In the meantime, we're told the theater has "beefed up" security around Fantasia -- and all over the venue -- and will be screening anything sent to Barrino's dressing room before it gets to her.
Fantasia tells TMZ, "I will not be defeated by one isolated person's hatred."
Taken from TMZ.com!
