Norimitsu Onishi / New York Times News Service

RICHMOND, Calif. — This small, blue-collar city best known for its Chevron refinery has become the unlikely vanguard for anti-corporate, left-wing activism in recent years.

It became the largest American city to be led by a Green Party mayor, who was re-elected two years ago even though the oil giant bankrolled rival efforts with $1.2 million. Social activists belonging to the Richmond Progressive Alliance gained control of the City Council, from where they have been taking on what they refer to as the “Chevron Man.”

But this election season, city leaders are fighting on two fronts, against not only Big Oil but also Big Soda, as they like to call their foes. If voters here approve a proposal on Tuesday’s ballot, Richmond will become the first city in the U.S. to add a tax on businesses that sell soda and other sweetened drinks.

Fierce campaigning has brought in the kind of money rarely seen in a community of 104,000 people. Soda companies have funneled $2.5 million into efforts to defeat the tax, while supporters have raised only $69,000.

In its continuing fight, Chevron has again spent $1.2 million, this time to oppose two council candidates critical of the company and to support three considered supportive.

Richmond, though, is not united. The two-pronged battle has sharpened the differences between the Richmond Progressive Alliance and leaders of the city’s growing Hispanic population and the once-dominant black establishment. Many in those groups oppose the soda tax and side with Chevron.