NEW YORK, Jan 8 (Reuters) - Three aircraft leasing companies on Tuesday filed a petition to force privately held Sun Country Airlines into bankruptcy court in an attempt to recover $3.1 million they claim is owed to them. Sun Country, which last month laid off most of its 900 workers and temporarily suspended its flights, said that it would appeal the validity of filing in Delaware and had 30 days to respond to the petition. The three firms, Pegasus Aviation, Pegasus Aviation Lease Asset Securitization Trust and Riverhorse Aviation Group, filed a petition in U.S. Bankruptcy Court in Delaware seeking to force Sun Country into involuntary Chapter 7 bankruptcy, according to court documents. ©2001 Reuters Limited.