Elon Musk and David Sacks Depart Fwd.us, Mark Zuckerberg’s Political Action Group

Elon Musk and David Sacks, two of the Silicon Valley stars behind Fwd.us, Facebook CEO Mark Zuckerberg’s political action committee, have left the group, according to sources familiar with the matter.

Musk made it clear that his departure was related to the PAC’s support of certain politicians whose positions on immigration reform and education jibed with the group’s aims, but whose record on environmental issues had come under fire.

“I agreed to support Fwd.us because there is a genuine need to reform immigration. However, this should not be done at the expense of other important causes,” Musk said in a statement to AllThingsD. “I have spent a lot of time fighting far larger lobbying organizations in D.C. and believe that the right way to win on a cause is to argue the merits of that cause. This statement may surprise some people, but my experience is that most (not all) politicians and their staffs want to do the right thing and eventually do.”

The group, spearheaded by Zuckerberg himself and launched in late March, aims to advocate for issues related to immigration reform and education, among other things. Along with former members Musk and Sacks, the group touts an all-star list of Valley luminaries, including LinkedIn’s Reid Hoffman, Yahoo’s Marissa Mayer and Kleiner Perkins’ John Doerr, among many others.

But Fwd.us has recently been criticized inside the Beltway and by some in Silicon Valley because of the group’s tactics and ties to conservative lawmakers on the Hill.

Environmentalist groups like the Sierra Club and League of Conservation Voters, as well as MoveOn.org and immigration-rights organizations like Presente.org, announced they would pull existing Facebook ads and hold any orders for new ones for a minimum of two weeks — a response to seeing Fwd.us-backed political ads for conservative lawmakers who support controversial policies like Arctic oil drilling and building the Keystone XL pipeline.

Musk, of course, is the CEO of Tesla Motors, which specializes in eco-friendly electric vehicles. He also sits on the board as chairman of SolarCity, a company focused on solar energy.

Sacks founded enterprise social network Yammer (sold to Microsoft in 2012) and was the creator financier and producer of “Thank You For Smoking,” a 2005 film that satirizes the life of a tobacco company spokesman “who spins on behalf of cigarettes while trying to remain a role model for his 12-year-old son,” according to the film’s IMDB description.

Facebook declined to comment. Microsoft and a Fwd.us spokeswoman did not immediately respond to requests for comment.