PORTLAND, Ore. (AP) — An Oregon ballot measure on the labeling of genetically modified foods is starting to attract big money.

The two opposing camps  on Measure 92 combined have reported contributions of more than $12 million — $5 million by labeling proponents, more than $7 million by opponents.

Similar measures in California and in Washington state failed narrowly in recent years after millions of dollars were spent, mostly by labeling opponents.

The anti-labeling campaign spent about $45.6 million in California, compared to $8.7 million by supporters. In Washington state, opponents spent $33.3 million, compared to $9.8 million by the pro-labeling groups.

If adopted, the initiative by Oregon GMO Right to Know would require manufacturers, retailers and suppliers to label raw and packaged foods produced entirely or partially by genetic engineering.

Ballots go out this week.