Voters in California and four other states on Tuesday could open a wider door to legalized recreational marijuana, posing substantial regulatory challenges and deepening the tension between state and federal drug laws.

Polls suggest legalization is almost a certainty in California, where medicinal use of the drug has been legal for nearly 20 years. Voters in Massachusetts and Maine also appear poised to approve recreational marijuana. Polls tracking similar measures in Arizona and Nevada, where voters are set to weigh legalized marijuana, show much tighter races. Voters in Florida are set to decidewhether to expand medicinal marijuana. Recreational marijuana use is legal in Alaska, Colorado, Oregon, Washington and the District of Columbia.