Pro-immigration reform forces, including some Republicans, are fighting to hold NumbersUSA in check.

They note that NumbersUSA, which shares a $6.5-million budget with a related foundation, seeks to drastically cut both illegal and legal immigration with the goal of stopping U.S. population growth. Some of NumbersUSA’s money comes from groups that support Planned Parenthood and other abortion rights groups that are anathema to many social conservatives, as well as environmental organizations that work on climate change.

“They are influential because they are masking themselves as conservative,” said Alfonso Aguilar, executive director of the Latino Partnership for Conservative Principles, a Washington-based advocacy group that works to integrate Latinos into the conservative movement. “Say where you stand on population control and global warming. You will see the reaction with conservatives. That’s the problem. The dishonesty.”

Critics on both the left and right say NumbersUSA’s clout has waned as public opinion has shifted. Last month’s 68-32 vote in the Senate to approve the immigration bill proved that, they say.

“While NumbersUSA might credit themselves with killing immigration reform in 2007, they can also credit themselves with helping Republicans lose the 2012 election” because of its hard-line stance, said Domenic Powell, senior organizer for Center for New Community, a Chicago-based advocacy group. “I think the Republican Party has recognized that and isn’t offering them the same echo chamber.”