Opponents of a proposed expansion of the state's bottle deposit law have poured another $2.4 million into a campaign to defeat the November ballot question.

The opponents, which includes supermarkets and the Washington-based American Beverage Association — had already spent $5.4 million to help pay for ads aimed at persuading voters to reject the proposal.

The question would expand the state's nickel deposit law to include bottled water and other non-carbonated beverages not included in the original law. It is Question 2 on the ballot.

Supporters of the question have raised about $525,000. The bulk of that has come from the Massachusetts Sierra Club.

Phil Sego of the Sierra Club said beverage companies are trying to buy the election.

Supporters say updating the decades-old law will reduce litter while critics say it will hurt small businesses.