For the third-straight year, former Alaska Gov. Sarah Palin has turned down an invitation to speak at one of the most high-profile conservative gatherings of the year.

Palin has declined an invitation to give the keynote address at the Conservative Political Action Conference (CPAC) in Washington next week citing scheduling conflicts. “February is our busiest winter month and with all the prior obligations and outside travel already scheduled for the month I had to forgo some of the opportunities in the Lower 48,” Palin told the Washington Post Thursday.

Palin has, however, accepted similar invites in the past, including the Southern Republican Leadership Conference (SRLC) in New Orleans last April. “I’m looking forward to addressing conservative activists from across the south at the 2010 Southern Republican Leadership Conference,” she said at the time. “This is a great opportunity to listen and speak to those who are helping to set the direction of our party.”

Palin’s continuing absence from CPAC has stirred up rumors that the one-time vice presidential hopeful does not want to be affiliated with the conference and its primary organizer, the American Conservative Union (ACU).

At the center of Palin’s decision may be the role David Keene, head of the ACU. According to Politico, Keene asked FedEx for $2-3 million last fall to gain the group’s support in a legislative battle with business rival UPS. At the time, a Palin spokeswoman responded to the move by simply affirming Palin’s support for “those who advance our core beliefs and lead by principle.”

While Keene has not directly responded to the accusations, he has characterized ACU’s relationship with Palin and her staff in the past as “very cordial and respectful.”

“Governor Palin has our admiration and we are disappointed that she will not be able to attend CPAC this year, but hope she will attend in the future,” Keene said.

While they may be “cordial” to one another, Keene has been a vocal critic of Palin in the past. In 2009, Keene told Newsmax magazine that Palin was “whining” about negative press coverage and that she was not ready to be a prime candidate.

“Conservatives like her, but you’ve got to have more than that,” Keene said. “You’ve got to be more than a rock star. If in fact she’s interested in the presidency, she has got to establish herself as someone you can envision in the Oval Office. And it’s become more difficult to envision than it was at the time of the election.”

Additionally, an aide to Palin last year criticized Keene and CPAC for putting “special interests over core beliefs” and “pocketbook over policy.”

“That’s not what CPAC should be about and people are tiring,” the source said. “Palin is taking a stance against this just as she did in Alaska.”

If she had agreed to deliver CPAC’s keynote address this year, Palin would follow the likes of conservative radio hosts Rush Limbaugh and Glenn Beck who have addressed the conference over the last two years, respectively.

Other possible candidates who are set to speak at CPAC next month include former Massachusetts Gov. Mitt Romney; former Minnesota Gov. Tim Pawlenty; former House Speaker Newt Gingrich; Mississippi Gov. Haley Barbour; Sen. John Thune, S.D.; Indiana Gov. Mitch Daniels; and former Sen. Rick Santorum, Pa.

However, Palin will not be the only well-known conservative to skip this year’s CPAC. Several others – including Sens. Jim DeMint and Marco Rubio – have announced that they, too, will be skipping the annual conference this year.