The US state of California has added an ingredient found in Roundup pesticide, manufactured by Monsanto, to its list of cancer-inducing chemicals, requiring the product to start carrying a warning label by January 2018.

Products containing the herbicide, glyphosate, would have to carry a warning label indicating that they are “known to the state of California to cause cancer and birth defects and other reproductive harm”, the Los Angeles Times reported on 27 June.

However, the decision would not ban the chemical from being used on the fields or sold in stores as the proposal did not set rules on how the listed products could be used.

The Los Angeles Times said that while federal and state officials had the power to ban glyphosate nationwide, they had not done so as, in their opinion, the chemical had so far been found to have low toxicity and it could be safely used on crops, in garden, park and golf courses, provided safety instructions were followed.

The US Environmental Protection Agency (EPA) arrived at a similar conclusion last year when it ruled glyphosate was not a carcinogen.

The EPA decision drew criticism from environmental organisations, which claim that Monsanto – which markets GM seeds modified to be resistant to its glyphosate-containing Roundup product, including soyabeans – is attempting to boost its profits by continuing to use the product.

The agency began the process to require a warning label on glyphosate two years ago, but it was brought to a halt when Monsanto sued the EPA.

The company may again resort to litigation as a Monsanto spokesman told the Los Angeles Times that it would “continue to aggressively challenge” the decision in California.