Fitch Ratings recently issued a warning that commercial real estate lending, which has reached record levels at banks, is unsustainable.

According to Fitch, CRE lending has risen at a nearly 4% compound annual growth rate over the past five years. Multifamily lending increased at a rate of 10.7% during the same period of time.

Small and midsize banks are believed to have the largest CRE exposure. The warning cited $205 billion in maturing loans from commercial mortgaged-backed securities that originated in 2006 and 2007 as creating further CRE loan growth in the near term.