The US House of Representatives has voted to repeal regulations that restrict how internet providers can use customer data.
The Senate has also voted to reverse the rules, and the White House says Donald Trump supports scrapping the restrictions that were approved under Barack Obama.
Currently, big internet providers including Verizon, Comcast and AT&T are limited in how they can use information such as customer browsing habits, app usage and location data.
Removing those limits would mean they could sell personal information to allow highly targeted advertising.
Leading Democrat Nancy Pelosi said the Republican-led effort was putting profits over the privacy concerns of Americans.
"Overwhelmingly, the American people do not agree with Republicans that this information should be sold, and it certainly should not be sold without your permission," she said.
"Our broadband providers know deeply personal information about us and our families."
The providers would not need permission to monitor and sell online behaviour information for marketing purposes.
Search engines and streaming sites already collect such data but providers have a far broader view of online behaviour.
The move would allow them to compete with the likes of Google and Facebook in the lucrative digital advertising market.
Although customers could choose to abandon their provider, privacy activists say there is often little choice within a specific geographical area.
They have called this a "tremendous setback for America" that would allow sensitive personal information such as health and financial details to be abused.
Proponents say current regulations stifle innovation, forcing providers to abide by strict guidelines.
They also claim scrapping the regulations would benefit consumers by allowing for more relevant advertising.
This latest Trump era attack on regulations is being seen as the first of many that could alter the future of the internet.