An indictment unsealed Tuesday alleges that the Binghamton Republican claimed he didn't know how his son, Matthew, got the job. It also says he told the FBI he was unaware that a lobbying firm was paying part of his son's salary.
It has been previously alleged that Thomas Libous arranged his son's job and salary in exchange for steering business to the law firm.
Libous' office said a statement would be issued later Tuesday. A message left at his lawyer's office was not immediately returned.
Mathew Libous was indicted on federal tax charges. A call to his attorney was not immediately returned.
The 61-year-old lawmaker has been undergoing treatment for metastatic cancer since he was diagnosed with prostate cancer in 2009. Last year, he stepped down as the Republican Party's campaign chairman, though many expected him to seek another term in the Senate this fall.
Libous orchestrated his party's return to power in the Senate in 2010. Yet he remained well liked by many on both sides of the political aisle in the contentious state capital. He was first elected to the Senate in 1988 and is currently the deputy majority leader.
The indictment is the latest in a series of criminal allegations that have dogged dozens of state lawmakers in recent years. Last week, Assemblywoman Gabriela Rosa pleaded guilty to federal charges that she got married to secure her legal residency and later citizenship.
Earlier this year, former Democratic state Assemblyman Eric Stevenson of the Bronx was sentenced to three years in prison for accepting bribes. Former Buffalo-area Assemblyman Dennis Gabryszak, a Democrat, stepped down in January after a series of sexual harassment allegations.