The documents, which were made public on Tuesday, are part of a mass litigation in federal court in San Francisco claiming Monsanto failed to warn that exposure to Roundup could cause non-Hodgkin's lymphoma, a type of cancer.

The company has denied that the product causes cancer.

Plaintiffs claim that Monsanto's toxicology manager ghostwrote parts of a scientific report in 2013 that was published under the names of several academic scientists, and his boss ghostwrote parts of another in 2000.

Both reports were used by the EPA to determine that glyphosate, a chemical in Roundup, was safe, they said. They cited an email from a Monsanto executive proposing to ghostwrite parts of the 2013 report, saying, "we would be keeping the cost down by us doing the writing" while researchers "would just edit & sign their names so to speak."