Corporations and some of the wealthiest Americans spent more than $1 billion over the past 18 months on ballot initiatives in just 11 states, according to campaign finance data, an explosion of money used to pass new laws and influence the public debate.

The initiative process was originally aimed at giving citizens the chance to break the hold that corporations had on state legislatures, but it is increasingly being used in reverse: Corporations and wealthy individuals are backing measures to get around reluctant legislatures.

The hardest-fought measure this year was in Washington state, where corporations spent more than $27 million on Initiative 522, which would have required labels on food that included genetically modified ingredients.