Coca-Cola spent $4.8 million through the second quarter of this year; PepsiCo spent $2.34 million; DuPont spent $2.4 million, while Monsanto spent $1.08 million, according to the report.
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 disclosed on lobbying the issue by food and biotechnology companies in 2013, according to EWG, a Washington-based nonprofit that supports GMO labeling.
Read MoreVermont becomes first US state to mandate 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.
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.
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. Last year, a group of international scientists said more independent research is needed on GMOS.
Read MoreBig lobbying dollars flow in engineered food fight
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.