In a letter to Congress, the groups ask lawmakers to vote against a proposal that would offer farms credits for conserving carbon or reducing their greenhouse gas emissions.

A coalition of environmental, agriculture and justice groups is attempting to drum up opposition to legislation that aims to help farmers store carbon in the soil, a practice that’s become a key piece of the Biden administration’s strategy on climate change.

In a letter sent to members of Congress this week, the groups urge lawmakers to vote against the Growing Climate Solutions Act, a bill first introduced last year that would help create a voluntary carbon market, in which polluting companies would offset their emissions by paying farmers to conserve soil in ways that store carbon or to take measures to reduce emissions on their farms.

The concept has become politically popular, gaining favor with both Democrats and Republicans, even those skeptical of the science on climate change.