The case is being handled by prosecutors in the Public Corruption Unit of U.S. Attorney Michael Garcia's office. Garcia spokeswoman Yusill Scribner said the office had no comment.
Spitzer, a Democrat, was the former attorney general of New York and earned a reputation for being tough on crime after taking on corruption on Wall Street. His first year in office, however, was rocked by scandal and allegations of dirty tricks.
As attorney general he prosecuted at least two large prostitution rings.
"This was a sophisticated and lucrative operation with a multitiered management structure. It was, however, nothing more than a prostitution ring," Spitzer said in 2004 after the bust of a 16-person prostitution ring in Staten Island.
Spitzer has a reputation as a loving father and is often seen in New York City and Albany with his three daughters.
"It is never pleasant to watch a public figure melt down," said Hank Sheinkopf, a veteran New York political consultant. "It is even less pleasant with Spitzer because what it says to us is that even a guy with as tough a moral fiber as him in fighting for public good became a victim to something within himself."
"This is a great shock and a great upset for his family, " Sheinkopf said. "He is a loving father who has been a doting father for his daughters and it must be very difficult for them."
News of the allegations shook the political world, with politicians and pundits from both sides of the aisle commenting.
Spitzer has endorsed New York Sen. Hillary Clinton for the Democratic presidential nominee.
At a pizza stop in Scranton, Pa., Clinton said she sent her best wishes to the governor's family and withheld judgment.
"I don't have any comment on that but I am obviously sending my best wishes and thoughts to the governor and his family. … Let's wait and see what comes out over the next days but right now I don't have any comment and I think that it's appropriate just to wish his family well and we will wait and see how things develop."
Sen. Charles Schumer, Clinton's Senate colleague, similarly demurred.
"I feel bad for him and his family but until he makes a more complete statement, I have nothing more to say," he said.
Additional reporting by Jennifer Parker.