More than 150 U.S. farm and food businesses and organizations on Wednesday called for the U.S. Department of Agriculture to strengthen its oversight of field trials of experimental, genetically modified crops.

The group includes organic and natural food industry representatives as well as family farm and trade policy players. It said the disarray in international markets after an unapproved genetically modified wheat developed by Monsanto Co was discovered growing unchecked in Oregon this spring is the latest example of the need to change GMO field trial regulations.

“There are major weaknesses in USDA’s oversight of experimental field trials, including how unauthorized crops are contained,” the group said in a statement issued in its behalf by the Organic Seed Alliance and the Rural Advancement Foundation International.

“Current U.S. policy includes neither mandatory contamination prevention measures nor an adequate system for monitoring the success of containment following trials,” the group said.

The group sent a letter to USDA Secretary Tom Vilsack in late July and met with him last week in Washington to discuss its concerns. In its letter it asked that USDA “fix its rubber-stamp approach to GE crops” and said that “improvements in regulations and oversight must start at the field trial stage.”

USDA spokeswoman Courtney Rowe said the meeting between Vilsack and the group was productive.

“We are currently carefully reviewing the concerns and information shared with us and will be responding in full in the near future,” Rowe said.

USDA told Reuters earlier this month that it has strengthened oversight of biotech crop field trials in recent years. The agency said it conducts about 700 inspections annually, up from about 500 in 2007, and has improved training for monitoring compliance with test protocols.

Field trial controls are of special interest to U.S. wheat growers because the April discovery of Monsanto’s unapproved wheat prompted some foreign buyers to temporarily refuse certain varieties.

Many foreign buyers have said for years that they do not want genetically modified wheat, and there was concern that the experimental wheat may have contaminated commercial wheat supplies. No genetically altered wheat is offered for commercial sale, though several companies continue to experiment with biotech strains.

Monsanto said it stopped its experiments with the wheat in question in 2004 and 2005 and has no idea how the biotech wheat came to be growing in Oregon this year. USDA has said it believes the incident was isolated and it reassured wheat buyers there is no sign of contamination in commercial supplies.

But several growers have sued Monsanto for negligence, and USDA has said it is still investigating the incident.

The group seeking tighter controls said it wants the government to halt any new approvals of GMO wheat field trials until the investigation into the Oregon contamination issue is completed.

There have been other episodes in which experimental biotech crops have eluded efforts to keep them contained.

A type of biotech rice developed by Bayer AG to resist herbicide was not approved for consumption but still showed up in the food supply in 2006. Its presence in the U.S. crop led Japan and the European Union to restrict U.S. rice from crossing their borders, triggering a plunge in rice prices. More than 7,000 long-grain rice producers claimed damages.

Traces of an unapproved genetically modified trait for corn were found in U.S. corn planted in 2006 and 2007.