A federal judge on Tuesday questioned a $2 billion proposal by Bayer AG (BAYGn.DE) that would create a framework for resolving future claims that its Roundup weedkiller causes cancer, casting doubt on the plan a day before a key hearing.

Bayer and class action attorneys hope U.S. District Judge Vince Chhabria in San Francisco will give preliminary approval on Wednesday to create a class of people exposed to Roundup who could get sick in the future.

The agreement would provide free medical exams and up to $200,000 in compensation if a class member is diagnosed with non-Hodgkin lymphoma, a cancer.

Chhabria in a court filing asked if it was possible to contact the potentially millions of homeowners and farmworkers who have been exposed to Roundup to notify them they were going to be bound by the settlement.