Organizing For Action, the non-profit group formed out of the Obama campaign, has stepped up its efforts against Republican members of Congress who don’t believe in climate change.

On Monday, the organization released a Twitter tool for supporters to “call out” their member of Congress as a “climate change denier,” with tweets like: “Rep. [John Doe] Stop denying the science of #climate change. It’s time for Congress to act.”

Organizing for Action was formed in January by former campaign aides as an advocacy group to push President Barack Obama’s agenda with a focus on immigration reform, gun control, and climate change. “OFA listed climate change as a priority on our first day,” a spokesperson for the group told TIME. “We believe that real change is not going to happen unless you first get the conversation in washington on climate change to at least start with agreeing its a problem.”

But the climate push is not tied to any specific legislation—because there is none in Congress—though it may be tied to the impending administration decision on whether to approve the Keystone XL pipeline, which would transport Canadian tar sands oil to the Gulf Coast. Strongly opposed by environmentalists, the pipeline has become a touchstone in the green community and a thorn in the side for the White House. Keystone politics followed Obama to a jobs event in Baltimore last week where the president of a company he was visiting to highlight manufacturing spoke out in support of the pipeline juts day earlier. Hundreds of pipeline opponents protested in front of an Obama fundraiser in New York last week.

But the Obama group has been silent on the issue, rebuffing calls to speak out against the pipeline in deference to Obama’s own silence waiting for the State Department to complete its review of the project. That decision is expected in the coming weeks, and if approved, Obama would be in the position of further angering a significant and vocal contingent of his liberal base.

OFA has tried to skirt the controversy by focusing on the climate deniers, releasing a video last month highlighting lawmaker statements on climate change. Former Obama campaign manager Jim Messina emailed a “tin foil hat alert” to the list about them as well, encouraging supporters to sign a petition encouraging them to embrace climate science.

The new Twitter tool links member statements on climate change—from floor speeches, news interviews, and public statements—with their Twitter handles, allowing OFA supporters to call out lawmakers by name.

“We will continue updating the list below as supporters get answers to the basic question of whether their representatives in Congress accept the science on climate change,” OFA wrote. ‘We hope that this list will shrink as members clarify what they truly believe about climate change.”