Washington (CNN) - A growing number of outfits are planning to boycott this year's Conservative Political Action Conference, the annual gathering of right-leaning activists in Washington known as CPAC, in part because organizers are welcoming a pro-gay Republican group into the fold.
And one of the groups pushing the CPAC boycott, the American Principles Project, took fresh aim at the conference Tuesday for inviting Indiana Republican Gov. Mitch Daniels, who angered many social conservatives last year by calling for a "truce" on social issues while the country works through its economic problems.
"Governor Daniels' selection is an affront to the millions of conservatives who believe that social issues such as abortion and traditional marriage are non-negotiable," APP's executive director Andy Blom said in a statement.
Blom told CNN he sees Daniels having a difficult time winning the GOP nomination, or the general election, without the help of social conservatives.
"He has flown his white flag and he has surrendered," Blom said. "The foot soldiers in the conservative movement have for so long been pro-lifers. You can't win a national election by throwing these people away. We aren't going to stand for it."
Other potential presidential contenders committed to speak at CPAC are Minnesota Gov. Tim Pawlenty, Mississippi Gov. Haley Barbour, former House Speaker Newt Gingrich, Sen. John Thune, Texas Gov. Rick Perry and Texas Rep. Ron Paul.
Daniels has sent strong signals that he intends to run but has pledged not to make a decision until after Indiana's legislative session concludes in April.
But while his fiscally conservative record has made him attractive to the economic wing in the party, other conservatives were baffled last June when he told the National Review that the next president "would have to call a truce on the so-called social issues."
Daniels has not backed away from that assertion, however, ominously comparing that the country's debt problem to the threat of an invading army massing at the border.
Aides to Daniels did not respond to a request for comment about APP's statement, nor did a CPAC representative.
CPAC, meanwhile, has continued to take heat from conservative groups upset over the inclusion of GOProud, the pro-gay Republican group, and the management style of American Conservative Union president David Keene, who runs the event.
Among the influential conservative groups planning to skip this year's event: The Heritage Foundation, Tony Perkins' Family Research Council, Brent Bozell's Media Research Center, and Concerned Women for America.
Blom said he believes those groups will hold something of a rival conference later this year built around the annual Values Voter Summit.