Washington State has signed a law that bars service providers from blocking websites or offering fast lane net access to companies willing to pay.
It is in direct opposition to the Federal Communications Commission regulator, which has moved to roll back net neutrality.
At least 20 other states are considering similar legislation.
Some states have banned agencies from doing business with broadband providers that don’t uphold net neutrality.
Net neutrality is the principle that all internet traffic should be treated equally.
In December the FCC voted to repeal the rules, in what was seen as a major victory for the telecoms industry.
Chairman Aji Pai argued that it would lead to greater investment in broadband infrastructure because service providers would have new avenues to make money.
But a vocal and growing list of opponents, including tech firms and public interest groups, have promised to mount legal challenges to preserve the rules which they say are at the heart of what makes for a fair internet.
Washington State governor Jay Inslee said at the signing ceremony: “We’ve seen the power of an open internet. It allows a student in Washington to connect with researchers all around the world – or a small business to compete in the global marketplace.
“It has allowed the free flow of information and ideas in one of the greatest demonstrations of free speech in our history.”
The decision in Washington means that internet service providers may have to have a different set of policies there compared to other states that they operate in.
Net neutrality supporters in Congress are trying to overturn the new law through legislation.
California is also considering its own state law to preserve net neutrality.
Senator Scott Wiener introduced the legislation in January, saying net neutrality “was essential to our 21st century democracy”.
“We won’t let the Trump-led FCC dismantle our right to a free and open internet, and we won’t let them create a system where internet providers can favour websites and services based on who pays more money.”
The final draft of the rules takes place on April 23, which will be the day the repeal takes effect.
The FCC has not responded to requests for comment.