* Aetna, UnitedHealth, WellPoint and Humana get letters
* House committee seeks answers by Sept. 14

WASHINGTON - Democrats leading the U.S. House of Representatives Energy and Commerce Committee widened their probe of the health insurance industry on Monday, seeking information on companies' policies for small businesses.

In letters sent to several insurers, including Aetna Inc (AET.N), UnitedHealth Group Inc (UNH.N), WellPoint Inc (WLP.N) and Humana Inc (HUM.N), Chairman Rep. Henry Waxman sought information on policies sold to businesses with 100 or fewer workers, citing concerns that insurers were terminating coverage when workers got sick and their claims increased.

Medica and Wellmark Blue Cross Blue Shield also received letters, which seek the information by Sept. 14. (Reporting by Susan Heavey, editing by Gerald E. McCormick)