The Environmental Protection Agency has re-approved weedkillers containing a contentious chemical for use on genetically engineered cotton and soybeans.

The decision, announced late Friday, faced immediate backlash from environmental groups as well as “Make America Healthy Again” activists who are aligned with President Trump and have called for tighter regulation of chemicals in the nation’s air and water and its food supply. Their criticisms of Trump administration policies are a sign of growing tensions among the president’s base of supporters.

A federal court had made certain uses of dicamba illegal in 2024 after some farmers complained that it tended to drift into neighboring farms and gardens, damaging crops that hadn’t been genetically engineered to resist it. It was the second time courts had vacated E.P.A. approvals of the weedkiller, each time citing risks that the herbicide would harm neighboring fields. The ban was scheduled to take full effect last year.

The E.P.A. subsequently reviewed dicamba’s uses and found it posed no risk to human health. On Friday, it said it was re-approving the chemical.

The agency’s decision was in response to advocacy from cotton and soybean farmers who relied on access to dicamba for controlling weeds, E.P.A. said in its Friday-evening statement. Its analysis had found that there was no unreasonable risk to human health and the environment so long as dicamba was applied according to instructions, the agency said.