SAN FRANCISCO (MarketWatch) -- CIT Group Inc., in one of the biggest corporate bankruptcies ever, filed for Chapter 11 protection in New York on Sunday.

CIT CIT, +2.72% , a major lender to small and midsize businesses, has struggled to avoid collapse since the recession triggered billions of dollars in loan losses and the financial crisis cut the company off from its main source of financing.

"The decision to proceed with our plan of reorganization will allow CIT to continue to provide funding to our small business and middle market customers, two sectors that remain vitally important to the U.S. economy," Chairman and CEO Jeffrey M. Peek said in a statement.

With roughly $60 billion in assets, CIT's filing is probably the fourth-largest bankruptcy in U.S. history, ranking between General Motors MTLQQ and Enron. The bankruptcy of Lehman Brothers LEHMQ, which collapsed last year, was the biggest.

CIT asked the U.S. government for a bailout earlier this year, but despite the company's large business-lending operations, it wasn't deemed too big to fail. See story on government rejecting CIT.

That contrasts with other financial-services companies like American International Group AIG, +0.87% , Citigroup C, +1.62% and Bank of America BAC, +1.34% , which have received more than $100 billion of government support since last year.

In October, CIT unveiled two different reorganization plans. One involved exchanging some debt, while the other was a voluntary pre-packaged bankruptcy restructuring. On Friday, activist investor Carl Icahn, a big CIT debt holder, said he was voting for the pre-packaged reorganization plan. That made such a filing more likely. See story on CIT's agreement with Icahn.

CIT was hit hard by the global financial crisis in two main ways. As the economy ground to a halt and unemployment surged, more of the company's loans went bad and it reported billions of dollars in losses over multiple quarters.

More importantly, CIT was one of the largest nonbank lenders in the world, a big part of the so-called shadow banking system that collapsed when the financial crisis erupted last year.

Roughly three-quarters of CIT's funding came from the unsecured debt market, but the company was shut out of this market as the crisis deepened. Bank deposits, considered a more stable source of money, made up 0% to 5% of CIT's funding.

CIT became a bank-holding company and got $2.3 billion from the government's Troubled Asset Relief Program in December. But that didn't solve its long-term problem: how to borrow money at competitive rates so it could continue lending.

CIT applied for a debt guarantee program run by the Federal Deposit Insurance Corp. but was rejected. Efforts to shift more of its assets to its banking unit, CIT Bank, have also hit hurdles.

CIT's bankruptcy will likely mean that the Treasury Department loses the $2.3 billion it invested in the company -- the biggest loss from TARP so far.