Puerto Rico Sen. Jorge de Castro Font was indicted by a federal grand jury on 31 criminal counts including bribery, wire fraud and money laundering, U.S. Attorney Rosa Emilia Rodriguez Velez said.
An aide to the senator, Alberto Goachet, was also charged in the alleged scheme to extort monthly payments from businesspeople on and off the U.S. Caribbean island, as well as from lobbyists with interests before the territory's government.
De Castro was arrested at his lawyer's office in San Juan, the capital, FBI spokesman Harry Rodriguez said.
The senator, who has denied any wrongdoing, stepped down as spokesman for the main opposition party after the FBI and the Internal Revenue Service raided his home and office in August, seizing computers and bags full of documents.
But he has refused to drop his bid for re-election in November. A judge recently rejected a petition from his New Progressive Party that sought to disqualify de Castro because of the corruption probe.
Earlier Thursday, de Castro said he met with officials from the island's Justice Department to provide sworn statements about wrongdoing involving the Senate. He did not give further details.
The FBI says the investigation is not related to a separate corruption probe targeting Gov. Anibal Acevedo Vila, who has been indicted on 24 federal counts including conspiracy to violate federal campaign laws and defraud the Internal Revenue Service. Acevedo is also seeking re-election next month.
Thursday's indictment accuses De Castro, 45, of extorting money that he used to pay expenses such as credit card bills, home utilities and clothing. He allegedly threatened to use his influence as chair of the rules committee to damage the interests of businesspeople if they refused to pay.
The indictment alleges that in one instance, he asked a person with business before the Senate to pay half his sister's salary at an advertising firm.
Several of the charges he faces carry a maximum sentence of 20 years in prison.