The US Supreme Court on Tuesday 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, AFP reported Tuesday.

The high court did not explain its decision, which left intact a $25 million ruling in favor 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 $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.

“The company believes that the decision undermines the ability of companies to rely on official actions taken by expert regulatory agencies,” it added, referring to a 2020 federal finding that Roundup’s active ingredient is not risky.