Club for Growth President Chris Chocola sent a letter this morning to Republican House leadership threatening to mobilize his group on behalf of Rep. David Schweikert should they show favoritism to Rep. Ben Quayle in what is going to be a brutal primary in Arizona’s 6th district.

Chocola urged neutrality, citing concerns about Majority Leader Eric Cantor (Va.) backing Rep. Adam Kinzinger (R) in an Illinois primary over Rep. Don Manzullo. Kinzinger defeated the veteran lawmaker Tuesday. Chocola then noted that Speaker John Boehner’s (Ohio) leadership political action committee made a donation to Quayle’s campaign prior to the release of Arizona’s redistricting map and the formation of the Schweikert-Quayle race.

“In the name of neutrality, we urge Speaker Boehner to contribute the same $10,000 to Rep. Schweikert that he has already given to Rep. Quayle,” Chocola wrote in the letter.

But then he took an ominous tone.

“Should it become apparent that you are choosing sides on behalf of Rep. Quayle, the Club for Growth PAC will consider it necessary to intervene on behalf of Rep. Schweikert,” Chocola wrote. “As is our practice, if the Club’s PAC entered this primary, it is highly likely that our 75,000 members would donate considerably more funds to Rep. Schweikert’s campaign than the Republican House leadership would contribute to Rep. Quayle’s campaign.

“It is our preference to remain on the sidelines of the Arizona race, as both candidates have fine records,” he added.

Roll Call rates the Arizona race as Safe Republican.