US Congressman Henry Cuellar and his wife have been charged with accepting approximately $600,000 (£478,000) in bribes, the Justice Department said.
The couple allegedly received corrupt payments from an Azerbaijani state-owned oil company and a Mexican bank.
The Texas Democrat denied the allegations in a statement.
The couple were released on bail after appearing in court in Houston. If convicted, they could face decades in prison.
“I want to be clear that my wife and I are innocent of these allegations,” Mr Guller, 68, said on Friday.
Each of the couple has been charged with conspiracy, bribery, wire fraud, money laundering and violating a ban on acting as agents of a foreign organization.
The Justice Department said the bribes were laundered from 2014-21 through a series of “sham consulting contracts” through middlemen and front companies owned by 67-year-old Imelda Cuellar.
In exchange for the money, Mr Cuellar agreed to influence US foreign policy in favor of Azerbaijan and to push for measures beneficial to the Mexico City-headquartered bank. .
The Gullars allegedly used the proceeds from the bribery schemes to pay off several debts and make purchases for their families.
According to the indictment, there were $58,000 (£46,000) in credit card payments, about $11,000 in car payments, $18,000 in wholesale purchases and $12,000 for a custom gown.
Senator Robert Menendez, a New Jersey Democrat, faces similar charges. He and his wife have been accused of using their influence to benefit the governments of Egypt and Qatar and receiving bribes in exchange for the senator.
In a statement released by his office, Mr Gullar pledged to continue campaigning for re-election in November.
“Before I took any action, I sought legal advice from the House Ethics Committee, who provided more than one written opinion and an additional opinion from a national law firm,” he said.
“The actions I took in Congress were consistent with the actions of many of my colleagues and were in the best interest of the American people.”
Mr Cuellar was a lawyer and former customs broker before entering politics. He was first elected to Congress in 2004 and is a former co-chair of the Congressional Azerbaijan Caucus.
Hakeem Jeffries, the Democratic leader of the House of Representatives, said Mr. Cuellar would take a leave of absence from his post on the Homeland Security Subcommittee while the case continues.
Mr. Cuellar’s home and campaign office in Laredo were raided in January 2022.
Officials said at the time that the raid was part of a federal investigation into Azerbaijan and American businessmen with ties to the country.
Mr Cuellar is widely regarded as a centrist and has been described as an anti-abortion House Democrat.
In 2022, he narrowly survived a primary challenge from Jessica Cisneros, a progressive candidate who once worked as an intern in his office.