Lenders initiated foreclosure proceedings against more U.S. homeowners in May, setting the stage for increases in home repossessions and short sales — scenarios that could further weigh down home values in coming months.

Default or scheduled-home-auction notices were filed for the first time against 109,051 homes last month. That's an increase of 12 percent from April and up 16 percent versus May last year, foreclosure listing firm RealtyTrac Inc. said Thursday.

The firm monitors documents filed on properties with mortgages that have gone unpaid. Once that process begins, homes can end up foreclosed-upon, sold at auction or via a short sale. A short sale is when the bank agrees to accept less than what the borrower owes on their mortgage.