Amazon is launching an aggressive public push to persuade voters in California to overturn a law that requires online retailers to collect sales tax and is seeking to block similar proposals in other states.

Since the retail site went live in 1995, Amazon has not had to collect taxes in states where it doesn’t have a physical presence. But the recent months, a growing number of cash-strapped states have begun to include Amazon affiliates in determining whether the e-commerce giant has a physical presence. As a result, the company cut ties with affiliates in California, Connecticut, Illinois and other states.

Amazon, in a letter to affiliates, called the new tax laws “unconstitutional and counterproductive.”

The Associated Press reported that Amazon has filed a petition at the California Attorney General’s Office seeking a referendum on the issue and is in the process of collecting the 500,000 signatures needed for the question to appear on the ballot.