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 LankfordJames Paul LankfordMcConnell: 'Whoever gets to 60 wins' on immigration GOP senators turning Trump immigration framework into legislation Fractured GOP struggles with immigration strategy MORE (R-Okla.) in their battle to succeed retiring Sen. Tom CoburnThomas (Tom) Allen CoburnPaul Ryan should realize that federal earmarks are the currency of cronyism Republicans in Congress shouldn't try to bring back earmarks Republicans should know reviving earmarks is a political nightmare 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.