WASHINGTON — Internet activists declared victory over the nation’s big cable companies Thursday, after the Federal Communications Commission voted to impose the toughest rules yet on broadband providers like Comcast, Verizon and AT&T to prevent them from creating paid fast lanes and slowing or blocking Web traffic.

The 3-2 vote ushered in a new era of government oversight for an industry that has seen relatively little. It represents the biggest regulatory shake-up to telecommunications providers in almost two decades.

The new rules require that any company providing a broadband connection to your home or phone must act in the “public interest” and refrain from using “unjust or unreasonable” business practices. The goal is to prevent providers from striking deals with content providers like Google, Netflix or Twitter to move their data faster.

“Today is a red-letter today for Internet freedom,” said FCC Chairman Tom Wheeler, whose remarks at Thursday’s meeting frequently prompted applause by Internet activists in the audience.

Verizon saw it differently, using the Twitter hashtag ThrowbackThursday to draw attention to the FCC’s reliance on 1934 legislation to regulate the Internet.

Net neutrality is the idea that websites or videos load at about the same speed. That means you won’t be more inclined to watch a particular show on Amazon Prime instead of on Netflix because Amazon has struck a deal with your service provider to load its data faster.

For years, providers mostly agreed not to pick winners and losers among Web traffic because they didn’t want to encourage regulators to step in and because they said consumers demanded it. But that started to change around 2005, when YouTube came online and Netflix became increasingly popular.