The European Parliament is being urged to examine allegations that Monsanto hid the dangers of one of its weedkiller products, according to AFP.
A U.S. firm from Los Angeles is pursuing a lawsuit against the company, claiming the components used in the agriculture giant's best-selling herbicide Roundup are not safe.
The firm Baum-Hedlund-Aristei-Goldman sent a letter and attached documents accusing Monsanto of acting with "corporate malfeasance."
The letter said Monsanto had been "ghostwriting scientific literature designed to make glyphosate look safe, bullying scientists that publish anything negative about their billion-dollar product, and colluding with regulators to ensure 'positive' assessments."
The request comes as the European Union debates the renewal of the license for the herbicide for another 10 years.
It urged the European Parliament to review Monsanto's "relationship" with the European Food Safety Authority, which ruled that glyphosate shouldn't be classified as a carcinogen.
The letter also asked the parliament to probe "Monsanto's sponsorship and implementation of ghostwritten scientific literature, specifically designed to influence European authorities."
The firm represents farmers and their families in a lawsuit that alleges that Roundup causes cancer.
Monsanto says its glyphosate "meets or exceeds all requirements for full renewal under European law and regulation" and that the renewal procedure has in "many respects been hijacked by populism."