The U.S. Environmental Protection Agency (EPA) is expected to announce by Friday whether it will continue to allow paraquat, an herbicide suspected of causing Parkinson’s disease, to be sprayed on U.S. crops. Use of the weed killer has recently soared in the United States, but it is banned in more than 70 other countries.

The decision would allow continued use of a cheap, broad-spectrum weed killer, which is extremely toxic if ingested or inhaled. Scientists and patient advocacy groups also say a mass of evidence from lab dishes, animals, and people—including a rigorous epidemiological study published last year—suggests exposure to paraquat very likely causes Parkinson’s, the fastest growing neurodegenerative disorder.