'Piolin' Sues -- I'm The Victim of a Spanish Radio SHAKEDOWN

Spanish radio superstar Piolin has filed a lawsuit against 6 former co-workers ... claiming they were all part of a diabolical plot to shake him down for roughly $5 mil by threatening to go public with false allegations of sexual harassment, TMZ has learned.

Piolin -- real name Eddie Sotelo -- claims 6 former Univision employees contacted him last week and offered to "seal their lips" if he forked over $4.9 million in hush money.

In his lawsuit, filed today in L.A. County Superior Court, Piolin claims the six had threatened to come forward with allegations that mirrored those of another Univision employee who recently accused the radio star of sexual harassment and workplace misconduct. Piolin claims the accusers "have attempted a naked money grab, but have sorely underestimated their target."

As we previously reported, the other Univision employee is Alberto "Beto" Cortez -- who complained to Univision honchos that Piolin would grab his ass and genitals when he would arrive to the workplace. He claims Piolin would also berate him with homophobic slurs.

Piolin adamantly denied Beto's allegations -- claiming Beto concocted the whole story in a pathetic attempt at a shakedown.

As for Piolin's new accusers -- the radio star acknowledges he made outrageous and sarcastic comments on the air ... but says, "Everyone knew this 'horseplay' was all in good fun." Piolin also believes his zany antics were part of why his radio show was a success.