Mark Zuckerberg’s political action committee has lost support from fellow entrepreneurs Elon Musk and David Sacks. (Justin Sullivan/GETTY IMAGES)

Disputes over a controversial oil pipeline have seeped into the debate over immigration reform, weakening a once-united lobbying front by technology executives in Silicon Valley.

Elon Musk, one of the nation’s leading proponents of “green” technology and clean energy, has split off from the political action committee he helped build with the group’s leader, Facebook founder Mark Zuckerberg. Launched in March, the group’s mission is to pursue immigration and education changes in Washington.

However, the organization, called, came under fire from environmental groups last week for bankrolling several ads for lawmakers who also support building the Keystone XL pipeline. That didn’t sit well with Musk, the owner of electric car company Tesla Motors, who has long pushed an green-friendly policy agenda.

A Tesla spokeswoman confirmed to Washington Post technology reporter Hayley Tsukayama that Musk has left the group, and revealed that a second member had pulled out, too. David Sacks, founder of social networking service Yammer and financer for the film “Thank You for Smoking,” has since been removed from the PAC’s Web site.

Musk confirmed in a statement to AllThingsD that his departure was tied to the group’s support for politicians “whose positions on immigration reform and education jibed with the group’s aims but whose record on environmental issues had come under fire.”

The departures are a blow to one of the most formidable campaigns for immigration reform targeting highly skilled foreigners, especially because they suggest disagreements among members over non-immigration issues could threaten the coalition. That may make it tricky for Zuckerberg to win support from both sides of the aisle in Congress.

Rohit Arora, chief executive of Biz2Credit, a loan marketplace for entrepreneurs, said Zuckerberg’s organization should have stuck solely to the immigration battle and avoided paying for broad political ads in the first place.

“One of the big issues with the flameout of is that they were employing old pork-style politics, which does not work any more,” Arora said. “While trying to support the cause the high skilled immigration is good for the country, trying to get support of the senators and congressmen by campaigning in favor of other issues they support like the Keystone pipeline and opposing Obamacare smells of old-style Washington politics.”

Zuckerberg and his team hope to persuade lawmakers to ease visa restrictions for highly skilled immigrants, especially those with advanced degrees in fields like science, technology, engineering and mathematics (known collectively as STEM). New York City Mayor Michael Bloomberg’s advocacy group, Partnership for a New American Economy, has been pushing the same agenda, with both groups arguing that American schools are not churning out enough skilled workers to meet demand from U.S. employers.

Critics point to a growing collection of research that suggests otherwise, including a recent study from the Economic Policy Institute, a think tank, which showed virtually no “skills gap” in the labor force.

They have pushed back against provisions in the Senate’s comprehensive immigration proposal, which would expand the visa program for highly skilled foreigners (the H-1B program), with an even steeper increase in the number of visas available for degree holders in STEM fields. Many have warned that the lobbying efforts to do so come from technology firms looking to employ cheaper labor in foreign countries.

The bill is currently being marked up by the Senate Judiciary Committee, where it has already been met with opposition from both Democrats and Republicans.

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