By Ben Geman - 03/11/10 04:45 PM EST
The two companies together have received tens of billions of dollars in federal loans in recent years to help stave off collapse.
“Given that recent U.S. Treasury reports indicate American taxpayers presently own more than 60 percent of GM, I question the propriety of GM’s continued membership and participation in USCAP,” Barton wrote.
Barton is a climate skeptic who argues that legislation that imposes caps on greenhouse gas emissions would cause economic harm.
Barton’s attack on the automakers' participation in USCAP follows the recent departure of oil majors BP and ConocoPhillips from the group. The oil companies have alleged that major House and Senate cap-and-trade plans would harm refiners. Royal Dutch Shell remains a member of the coalition, which also includes several large utilities and other companies.