Former Vice President Al Gore and several liberal attorneys general are stepping up their attack on companies and organizations that question global warming, using “McCarthy-style tactics” to criminalize critics and their supporters, according to one target.

The well-respected Washington-based Competitive Enterprise Institute said Friday that it has been hit with a subpoena for climate research documents and even donor lists from 1997-2007 from one of the attorneys in the Gore group. CEI was given three weeks to provide the 20-year-old documents.