WASHINGTON — Tech companies and internet providers are poised for another dramatic showdown as the head of the Federal Communications Commission revealed a plan Wednesday for rolling back his predecessor’s rules mandating a free and open Internet.

The proposal from FCC Chairman Ajit Pai marks the first step toward undoing a key decision of the Obama era, one that forced Internet providers to behave more like legacy telephone companies. The stricter rules for ISPs had made it illegal to block or slow down websites for consumers – and they paved the road for other policies, such as one governing online privacy, which was overturned in a separate controversial move by Congress and President Trump earlier this year.

Pai’s attempt to reverse the net neutrality regulations rekindles a high-stakes debate over the future of the web. Internet providers argue they need weaker rules in order to continue upgrading their networks and to find new ways of making money. Consumer groups say giving ISPs freer rein will cause them to abuse their powerful position as gatekeepers between customers and the rest of the Internet, controlling what Web users can see and do, and at what cost, online.

Pai said that his agency’s net neutrality rules were “all about politics,” in a speech at the Newseum in Washington on Wednesday.

“Two years ago, I warned that we were making a serious mistake,” said Pai. “It’s basic economics: The more heavily you regulate something, the less of it you’re likely to get.”

Pai’s proposal is set for a vote at the FCC’s May 18 open meeting. If it is approved, Pai will begin seeking public feedback on the plan, which calls for regulating ISPs more lightly and asks Americans for ways to preserve the core principles of net neutrality while giving ISPs greater flexibility.

Internet activists are gearing up for a war of public opinion over the proposal. The last time the FCC considered the rules, in 2015, critics and advocates of net neutrality flooded the FCC’s electronic systems – submitting millions of comments, and setting an agency record, before the creaky database ground to a halt.

“Millions of people engaged in 2014-2015 to make sure these rules were instituted in the first place,” said David Segal, executive director of the advocacy group Demand Progress. “As Trump and his FCC seek to roll back the rules and let corporations manipulate Internet traffic in service of private profit, I’m sure we will see millions of Americans fight back.”

The stakes are as high as ever, as Republicans and broadband companies prepare to overturn an aspect of the policy they dislike the most: The classification of ISPs as “common carriers.” In a move led by Pai’s Democratic predecessor, Tom Wheeler, that decision triggered a change in how the government may regulate the industry.

Classifying ISPs as common carriers enabled the government to legally ban some practices, such as the outright blocking of internet traffic. And it also allowed the FCC to investigate other practices it viewed as potentially anticompetitive – such as when companies like AT&T and Verizon began exempting certain proprietary apps from their own wireless data limits. Critics of that tactic, known as zero-rating, say allowing it could give telecom companies the power to pick winners and losers in the Internet ecosystem.

Internet providers feared that the FCC could someday use its common-carrier authority to impose direct price regulations on the broadband industry. While the FCC under Wheeler refrained from doing so, the industry fought back with a high-profile lawsuit and allegations that the net neutrality policy was dampening network investments.

Tech companies nationwide have urged the FCC to keep the rules in place. Etsy, Vimeo, the startup incubator Y Combinator and 800 other startup firms sent a letter to Pai on Wednesday arguing that weakening the net neutrality rules would allow ISPs to “impede traffic from our services in order to favor their own services or established competitors.”

Earlier this month, Pai visited Facebook, Apple and other major firms to discuss his plan, as well as groups representing the cable and cellular industries. Although Pai had initially considered repealing the 2015 common carrier decision as part of his plan, he said Wednesday that the best path forward was not such an aggressive step, but an “open and transparent process.”

With the fate of a major Internet policy in the balance, Pai’s proposal may lend momentum to U.S. lawmakers who have proposed replacing the current FCC rules with congressional legislation. Republican members of Congress have said they are ready to craft a bill that enshrines some of the existing regulations permanently into law. But that effort is expected to stall without support from Democrats, such as Sens. Ed Markey of Massachusetts and Ron Wyden of Oregon who argue the FCC can and should regulate ISPs more heavily.

Some Democrats, such as Sen. Richard Blumenthal of Connecticut, signaled on a call with reporters Wednesday that they would support litigation against Pai’s FCC to defend the net neutrality rules – much as broadband industry advocates sued to overturn the regulations in 2015.

But opponents of the FCC’s regulations say the government should not replace the net neutrality regulations at all.

“The government should do nothing,” said Daniel Berninger, a network engineer who joined ISPs in suing to overturn the FCC’s rules. “The government did nothing from 1995 to 2015, and everything worked fine.”

Federal Communication Commission Commissioner Ajit Pai speaks during a Feb. 26, 2015, open hearing and vote on “Net Neutrality” in Washington. Tech companies are readying for a showdown with a Republican-controlled government over threats to net neutrality, a key issue for them and their users.