A powerful US senator who was indicted last month on corruption charges was hit with an additional charge on Thursday — allegedly acting as an unregistered agent of Egypt.

Senator Bob Menendez, 69, who has stepped down “temporarily” as head of the Senate Foreign Relations Committee, has pleaded not guilty to allegations that he took actions on behalf of Egyptian officials in exchange for bribes. He has defied calls to resign.

A superseding indictment filed by prosecutors on Thursday accused Menendez, his wife, Nadine Menendez, 56, and Wael Hana, an Egyptian-American businessman, of failing to register with the US government under the Foreign Agents Registration Act.

Menendez, a Democrat from New Jersey, is accused of accepting hundreds of thousands of dollars in bribes, including gold bars and a Mercedes Benz automobile, between 2018 and 2022 in exchange for using his influence on behalf of the Egyptian government.

According to the indictment, Menendez “took a series of acts on behalf of Egypt, including on behalf of Egyptian military and intelligence officials, and conspired to do so with” his wife and Hana.

It was the second corruption indictment in eight years against the veteran New Jersey politician and the case threatens his hold on his seat in Congress and the Democratic Party’s slim majority in the Senate.

Democrats head into the 2024 elections with a narrow 51-49 majority in the Senate.

Prosecutors said they found more than a half-million dollars in cash in Menendez’s New Jersey home and in his wife’s safe deposit box, allegedly received from three New Jersey businessmen seeking his help.

Menendez took the money to help protect two of the businessmen from Justice Department investigations, and to help the third, Hana, with a business monopoly granted to him by the Egyptian government, the indictment said.

Menendez, his wife, Hana and the two other businessmen, Jose Uribe and Fred Daibes, were charged with two counts of bribery and fraud. Menendez and his wife were also charged with extortion.

If found guilty, the most serious of the charges can bring up to 20 years in prison.

A senator since 2006 and before that a member of the House of Representatives for 14 years, Menendez has been a Democratic stalwart in Congress for three decades.

In 2015, he was charged with accepting bribes of private flights, luxury vacations and over $750,000 in illegal campaign donations.

But the charges were dismissed three years later after a deadlocked jury could not reach a verdict.