What law was violated? What crime did he commit? From what I understand, the problem was; practicing law, without a law degree. Which, as far as I'm aware, isn't a crime.
The quote is...
"Michael James Ross, you're under arrest for conspiracy to commit fraud."
"By my estimation, you've worked on 88 legal cases in your so-called career, and you committed fraud every time you picked up the phone, mailed a letter, signed your name, or appeared in court. Each instance carries a nine-month sentence, and to tell you the truth, I am too tired to do the addition."
In the gasp-inducing season 5 finale, the smooth-talker with the photographic memory, portrayed by actor Patrick J. Adams, was handed down a two-year sentence for fraud after practicing law without a degree for the last five years.