WASHINGTON, June 21 — The US Supreme Court today declined to hear a bid from Bayer-owned Monsanto that aimed to challenge thousands of lawsuits claiming its weedkiller Roundup causes cancer, a potentially costly ruling.

The high court did not explain its decision, which left intact a US$25 million (RM109 million) ruling in favour of a California man who alleged he developed cancer after using the chemical for years.

The decision marks a major blow to the German conglomerate’s legal fight against Roundup-related cases, and Bayer has set aside more than US$15 billion to deal with a wave of US lawsuits linked to the weedkiller.

"Bayer respectfully disagrees with the Supreme Court’s decision,” the company said in a statement.

Bayer has been plagued by problems since it bought Monsanto, which owns Roundup, in 2018 for US$63 billion and inherited its legal woes.

The German firm says it has not committed any wrongdoing, and maintains that scientific studies and regulatory approvals show Roundup’s main ingredient glyphosate is safe.

Glyphosate is nonetheless classified as a "probable carcinogen” by the International Agency for Research on Cancer at the World Health Organisation (WHO). — AFP