Aby Rosen and Michael Fuchs’ RFR has reportedly been defaulting on rent since May – crumbling yearslong negotiations with the private Manhattan college, a source close to the matter told The

Cooper Union sent RFR, the ground lease holder, a 10-day termination notice after the firm missed payments in June and July.

A partnership led by RFR Holding has held the ground lease to the Chrysler Building for the past five years, but it stopped making rent payments after May, according to Cooper Union, the private college that owns the land at 405 Lexington Ave.

Cooper Union took action to terminate RFR Holding’s ground lease on the Chrysler Building, but RFR wants to block that move.

Elsewhere in the city, lenders and city agencies have sued RFR for missed loan and tax payments at 17 State St., 522 Fifth Ave. and 90 Fifth Ave. The jewel in Rosen’s crown, the Seagram Building, carries nearly $1 billion in mortgage and mezzanine debt that must be refinanced next year. RFR controls nearly 3 million square feet of commercial space.

The owner of the land beneath the historic Chrysler Building said Friday it was taking control of the office tower, in what would be one of the most prominent buildings in the U.S. to be lost during the office-market collapse.