There are reports of Google and Yahoo leaving or threatening to leave the US Chamber of Commerce (a private lobbying organization, btw) because of its stance on certain legislation:

http://thinkprogress.org/economy/2011/11/04/361469/google-le...

http://www.fixtheuschamber.org/tracking-the-chamber/yahoo-jo...

Interesting progression of events in the last 15 years, given that anti-piracy legislation was originally written to protect software companies.