When it comes to avoiding the requirement of collecting sales tax from its consumers, Amazon is not afraid to open its wallet.

More than nine months before a proposed June 2012 referendum asking that California’s new Internet sales tax law be overturned, Amazon, the Seattle-based online retailer, has already spent $5.25 million, state records show, more than any company has spent in California this far from a vote in at least a decade.

“The initiative and referendum process have been hijacked,” said Loni Hancock, a state senator from Berkeley, who wrote the law Amazon is trying to overturn and who is now pushing legislation that could block Amazon’s referendum effort.

Even by California’s expensive campaign standards, the company’s early contributions are causing observers to take note.