In news that may presage bankruptcy for a mortgage lender with otherwise stellar asset quality, Thornburg Mortgage said yesterday that it had received a notice from JPMorgan Chase earlier this week claiming an "event of default" under a repurchase agreement with the Wall Street bank after failing to meet a $28 million margin call. In a filing with the Securities and Exchange Commission late Wednesday, Thornburg said that JPMorgan will "exercise its rights under the agreement." The Wall Street firm lent the troubled ultra-prime lender $320 million, Thornburg said. "The company’s receipt of the notice of an event of default has triggered cross-defaults under all of the company’s other reverse repurchase agreements and its secured loan agreements," Thornburg said in its filing with the SEC. Full details were not provided, but the company described its exposure under the now-defaulted repurchase agreements as "material." A call to the company for comment was not immediately returned. On Monday, Thornburg warned that it had received nearly $600 million in margin calls since the middle of February on its portfolio of Alt-A mortgage-backed securities, and that it was unable to meet all of the calls. Recent industry speculation has centered around rumors that some large holders of RMBS securities have become forced sellers in recent days, driving down the price of mortgage-backed securities like those held by Thornburg. The company's stock dropped more than 60 percent in pre-market trading Thursday, falling to $1.36. Disclosure: The author held no positions in Thornburg when this story was originally published. HW reporters and writers follow a strict disclosure policy, the first in the mortgage trade.