"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, the Los Angeles Times reported Saturday.
Billionaire Musk, who co-founded Pay-Pal, Tesla Motors and is the chief executive officer of Space Exploration Technologies, is one of two prominent Silicon Valley entrepreneurs to defect from Fwd.us recently.
The political group co-founded by Facebook CEO Mark Zuckerberg, has run television ads that attempt to reach out to conservative politicians, including one that applauds support of the controversial Keystone XL pipeline.
The ads have drawn criticism from environmentalists and other liberal groups, the Times said.
In a reaction to the criticism, Musk has left the Fwd.us group, as has David Sacks, CEO and founder of Yammer.
"We recognize that not everyone will always agree with or be pleased by our strategy -- and we're grateful for the continued support of our dedicated founders and major contributors," a Fwd.us spokeswoman Kate Hansen said in a statement.
"Fwd.us remains totally committed to supporting a bipartisan policy agenda that will boost the knowledge economy, including comprehensive immigration reform," Hansen said.