Loan sharking is a common underworld operation, but since it is the act of lending money is it actually illegal?

I'm sure there are laws to govern people that are in the ligitimate business of loaning money because of the records they have to keep and report to the IRS but I'm not sure they put a ceiling on the interest rates they charge. I think what makes a loan shark and what makes these dealings part of the underworld is the collection methods they use should you not pay them back - those are violent and deffinitely illegal.

Some would say "legal" businesses that charge exorbitant interest rates from desperate people are criminals also, but these parasites hide under the legalities & red tape of it all.