An environmental activist group has filed a legal petition with the U.S. Department of Agriculture seeking new rules that would enhance job protection for government scientists whose research questions the safety of farm chemicals.

The action filed on Thursday by the Public Employees for Environmental Responsibility, an advocacy group for local, state and federal researchers, came less than a week after a World Health Organization group found the active ingredient in Roundup, the world's best selling weed killer, is "probably carcinogenic to humans." Roundup is made by Monsanto Co.

The petition to the USDA presses the agency to adopt policies to prevent "political suppression or alteration of studies and to lay out clear procedures for investigating allegations of scientific misconduct."

According to the petition, some scientists working for the federal government are finding their research restricted or censored when it conflicts with agribusiness industry interests.

A USDA spokesman said the agency values the integrity of its scientists and the quality of their research.

The USDA denied that it needed to strengthen its rules and said it has a system in place to protect it scientists. An agency spokesman confirmed that from May 2013 through April 2014 eight complaints were filed. Five of those were deemed worthy of investigation and one was deemed to have merit, the agency spokesman said.

The complaints were filed through a new protocol the USDA implemented in 2013 specifically to protect the integrity of its scientific research.

PEER's Executive Director Jeff Ruch said on Friday that at least 10 USDA scientists have been investigated or faced other consequences arising from research that called into question the safety of certain agricultural chemicals.

Ruch said his organization had received mounting complaints over the last year from USDA scientists claiming they have been ordered to retract studies, water down findings, remove their names from authorship and experienced delays in approvals for publication of research papers. The petition does not identify any specific research or scientists.

"They have very little in the way of legal rights and have career paths that are extremely vulnerable," Ruch said.

Research into glyphosate, the key ingredient in Monsanto's Roundup herbicide, and neonicotinoid insecticides, which have been linked to honey bee and monarch butterfly endangerment, face particular scrutiny, Ruch said.

One senior scientist at the USDA's Agricultural Research Service told Reuters he has experienced harassment and censorship.

"Your words are changed, your papers are censored or edited or you are not allowed to submit them at all," said the scientist, who asked not to be named.