WASHINGTON -- A conservative advocacy group warned GOP leaders on Wednesday that they need to stay neutral in an Arizona congressional race featuring two Republican incumbents -- Reps. David Schweikert and Ben Quayle -- or else it would intervene with considerable financial resources on Schweikert's behalf.

The president of the Club for Growth, Chris Chocola, said the group would like to stay neutral in the race. But Chocola noted that House Speaker John Boehner through his leadership PAC had already donated $10,000 to Quayle's campaign. It called on Boehner to do the same for Schweikert.

"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 said in a letter to GOP leaders in the House.

The Club for Growth has tried to steer GOP to the right through aggressive fundraising for candidates that seek lower income taxes and less government. Its support can give candidates a substantial fundraising edge as members of the group donate to the candidate as well.

The two lawmakers are running in the state's newly drawn 6th Congressional District, which includes parts of Phoenix and Scottsdale. The primary is Aug. 28.

Chocola said that Schweikert had taken stands the Club for Growth supports even when members of his own party pressured him to do otherwise. If the same leaders attempt to defeat him, the group would vigorously come to his defense.

"It is our preference to remain on the sidelines of the Arizona race, as both candidates have fine records," Chocola said. "However, we will not sit back and allow House Republican leaders to invest resources with impunity against an incumbent fiscal conservative like Rep. David Schweikert."