By Jessica Sier

Bayer AG shares slumped Tuesday after a U.S. judge questioned part of the company's recent multibillion-dollar settlement over its glyphosate-based weed killer Roundup.

Californian Judge Vince Chhabria, who is responsible for settling future damages claims, expressed concern about the appropriateness of the settlement that the German chemical company agreed to in late June.

"The Court is skeptical of the propriety and fairness of the proposed settlement, and is tentatively inclined to deny the motion," the judge said, according to a filing published Monday evening.

At 1027 GMT, Bayer shares were down 6.9% at EUR62.43, the largest decline in Germany's DAX index.

Bayer has been hounded by the glyposate-based product since it took over U.S. agrichemicals company Monsanto in 2018, an acquisition that included Roundup and thousands of related lawsuits. Uncertainty over how the litigation issue would be resolved was alleviated in late June when the company struck a $10.9 billion settlement deal in the U.S.

As part of the settlement, it was agreed that for potential future cases a scientific panel would decide whether Bayer's product actually causes non-Hodgkin's lymphoma.

However, Judge Chhabria expressed doubts as to whether it was right to take this question out of the courts and delegate it to scientists, among other issues.

Bayer said it appreciates the judge raising his preliminary concerns.

"We take [this] seriously and will address at the preliminary approval hearing on July 24," the company said in a statement. 



  Write to Jessica Sier at jessica.sier@wsj.com