By Carey Gillam

(Reuters) - Opponents of mandatory labeling for foods made with genetically modified organisms spent more than $27 million in the first six months of this year on GMO-related lobbying, roughly three times their spending in all of 2013, according to an analysis released Wednesday.

The Grocery Manufacturers Association (GMA) and major food makers such as Coca-Cola Co and PepsiCo Inc and top biotech seed makers Monsanto Co and DuPont were among heavy spenders on GMO labeling-related lobbying, among other food issues, according to a report issued by the Environmental Working Group.

The group analyzed lobbying disclosure forms that cited labeling of foods containing genetically modified organisms (GMOs) along with other policy issues.

All told, the opponents of GMO labeling disclosed $15.2 million in lobbying expenditures for the second quarter of 2014, bringing the six-month total for 2014 to $27.5 million. That compared with $9.3 million reported in 2013, according to EWG, a Washington-based nonprofit that supports GMO labeling.

In contrast, supporters of GMO labeling disclosed $1.9 million in lobbying expenditures for the first half of 2014, up slightly from $1.6 million spent in 2013.

Mike Gruber, vice president for government affairs for the Grocery Manufacturers Association, said that the EWG report is “grossly misleading.” The lobbying work the dollars in the report includes a host of issues unrelated to GMO labeling, he said.

GMA said the dollars spent lobbying on GMO issues are far less than what the EWG report indicates.

"The GMO issue is a very important issue without a doubt but so is food safety… so is international trade," said Gruber.

The expenditures by food and biotechnology companies come as the group pushes for passage of a bill introduced in April by U.S. Representative Mike Pompeo that would block state laws that require GMO labeling on food packages.

Vermont in May became the first U.S. state to pass a mandatory GMO labeling law that requires no other trigger to become effective. More than 20 other states are considering mandatory labeling of GMO foods, including Colorado and Oregon, which have the issue on the ballot for the November election.

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Consumer groups and lawmakers pushing for mandatory labeling of GMOs say there is no scientific consensus on their safety, and consumers have the right to know if GMOs are in the food they eat. They say high pesticide use associated with GMOs and pesticide residues on food containing GMOS is a health concern.

But the food and agriculture industries, including the makers of genetically modified corn, soybeans, canola and other crops widely used in packaged foods, say their products are proven safe. They have sued to block the Vermont law and say that labeling will imply GMO products are unsafe, confuse consumers and increase costs for consumers as well as farmers and food companies.

(Reporting by Carey Gillam in Kansas City; Editing by Cynthia Osterman and Lisa Shumaker)