The Tea Party group FreedomWorks is adding its name to the long list of conservatives backing Oklahoma House Speaker T.W. Shannon (R) against Rep. James Lankford (R-Okla.) in their battle to succeed retiring Sen. Tom CoburnTom CoburnThe more complex the tax code, the more the wealthy benefit Congress, stop using our nation's military policy for political purposes Congress must rid itself of political 'pork' to preserve its integrity MORE (R-Okla.).

The group joins the Senate Conservatives Fund, Sens. Ted Cruz (R-Texas) and Mike Lee (R-Utah), and former Alaska Gov. Sarah Palin (R) in backing Shannon, who has quickly become anti-establishment Republicans' favorite in the race.

"T.W. Shannon is a principled leader who doesn’t simply talk about small-government reforms, he works to make them a reality," FreedomWorks President Matt Kibbe said. "We have enough talkers in Washington — it's time to send more leaders like T.W. Shannon who will get things done."

Lankford, a member of House GOP leadership who has compiled a conservative voting record in the House, has the backing of former Arkansas Gov. Mike Huckabee (R).

The primary is in late June.