(Reuters) - All 50 states launched a joint investigation of the mortgage industry on Wednesday, a move some experts fear will cause uncertainty and threaten the recovery of the fragile housing market.

The state attorneys general are looking at allegations some banks used shoddy or fraudulent paperwork to remove struggling borrowers from their homes during a foreclosure crisis that is one of the most visible wounds of the 2007-2009 recession.

"We are in the fourth year of a housing and economic crisis that was brought on by lax practices of the mortgage lending industry," Minnesota Attorney General Lori Swanson said in a statement. "The latest allegations of corner cutting and slipshod paperwork are troubling, but perhaps not surprising."

Industry experts warn the investigation could put the brakes on foreclosure proceedings. One of every four homes sold in the second quarter was a foreclosed property and any slowing could have an impact on the broader economy, as the housing market traditionally drives recoveries after a downturn.