U.S. Sen. Richard Blumenthal, D. Conn., is fighting a subpoena that would force him to give deposition testimony and turn over documents in a labor dispute between health care management companies and unions.

Blumenthal isn’t directly involved in the labor dispute, but according to court papers he filed earlier this week in the U.S. District Court for the District of Columbia, he has publicly supported the unions. The health care companies accused the unions of providing misleading information to influence public officials, and subpoenaed Blumenthal to find out what he was told.