This is what happens when you make the Internet mad.

On Wednesday, a group of technology companies began an unusual form of protest: The firms shut down or replaced the content on their own popular Web sites with protest messages to show their unhappiness with two Internet-regulation bills grinding through Congress. They argue that the bills would impose huge regulatory costs and stifle innovation on the Web.

Around the country, Americans woke up without some of the oddball essentials of online life. No Wikipedia. No Reddit, a compendium of links to stories and funny pictures that draws millions a day. And no I Can Has Cheezburger?, the world’s best-known collection of funny cat pictures.

Related: How to get around the blackout

In Washington, however, Wednesday has another significance.

It culminates a surprising lobbying effort in which technology companies such as Twitter, Wikipedia and Google have used their massive reach into Americans’ daily lives as a political weapon, to whip up support from online users.

In this fight, they were pitted against traditional Washington heavyweights, such as Hollywood and the recording industry.

And even before the LOLcats went on strike, it seemed as though the tech companies were winning.

This fight is over two similar bills: the House’s Stop Online Piracy Act and the Senate’s Protect IP (intellectual property) Act. Both are meant to attack the problem of foreign Web sites that sell pirated or counterfeit goods. They would impose restrictions forcing U.S. companies to stop selling online ads to suspected pirates, processing payments for illegal online sales and refusing to list Web sites suspected of piracy in search-engine results.

The idea is to cut off the channels that deliver American customers, and their money, to potential pirates. But tech companies see the laws as a dangerous overreach, objecting because, they say, the laws would add burdensome costs and new rules that would destroy the freewheeling soul of the Internet.

“The voice of the Internet community has been heard,” Rep. Darrell Issa (R-Calif.), who sided with the tech companies, said in a statement. Issa said he had already been told of a victory: GOP leaders told him that the House would not vote on a version of the bill that those companies oppose. “Much more education for Members of Congress about the workings of the Internet is essential.”

The biggest impact of Wednesday’s blackout may be in the shutdown of the English-language version of Wikipedia, which gets 2.7 billion U.S. visitors per month.

“It is the opinion of the English Wikipedia community that both of these bills, if passed, would be devastating to the free and open web,” said a statement signed by three of the free encyclopedia’s administrators, with the handles “NuclearWarfare,” “Risker” and “Billinghurst.” They said the decision to shut down the English-language portion of the site, starting at midnight Eastern time, had been made after a virtual discussion that involved 1,800 users.

But already, the momentum of the two controversial bills has been largely halted. Just weeks ago, they seemed on their way to passage, having cleared a Senate committee and garnered bipartisan support in the House.

Now, there is a bipartisan retreat. Sen. Benjamin L. Cardin (D-Md.), who co-sponsored an earlier version of the bill, has announced his opposition. Six Republicans on the same Senate committee — all of whom voted for the bill before — have written Majority Leader Harry M. Reid (D-Nev.) to ask that he slow the bill down, so it can be modified and considered later.

“We have increasingly heard from a large number of constituents and stakeholders with vocal concerns about possible unintended consequences of the proposed legislation,” the six wrote. They included Sen. Charles E. Grassley (Iowa), the ranking Republican on the Senate Judiciary Committee.

In the back offices of the Senate, many longtime aides were amazed at how quickly a new lobbying force had managed to outmaneuver experienced heavyweights. Sites such as Wikipedia and Tumblr had encouraged users to contact legislators, resulting in a flood of unhappy calls.

One Republican aide said that “SOPA” had already become “a dirty word beyond anything you can imagine.”

Both of the bills would allow the Justice Department to seek an injunction in court, barring U.S. sites from processing payments for a rogue Web site, selling it ads or listing its link among search-engine results.

“There’s no fundamental First Amendment right to engage in thievery. Nor to advertise thievery,” said Howard Gantman, at the Motion Picture Association of America. He said that the Internet’s free-for-all nature should not allow U.S. companies impunity to deal with crooks.

“Do we want to have laws?” Gantman said. “Or do we want to just say it’s a free-for-all Wild West?”

In addition to the costs, however, the tech companies say they would have to police vast sites full of user-generated content. They also objected to a provision that would have stripped the rogue sites out of the Internet’s virtual phone book. If a U.S. user entered the Web address, it would appear the site didn’t exist.

That provision “says that we’re no longer committed to the idea that there’s one Web. We’re no longer committed to the idea that any one person, anywhere in the world, can reach any one site anywhere else in the world,” said Sherwin Siy, of the nonprofit advocacy group Public Knowledge.

Over the weekend, the tech companies won a major victory. White House officials signaled concerns about the phone-book provision. The bill’s sponsors had already said they would remove it.

But several companies say they still have significant problems with the bill. They say the bill spreads culpability too widely and could leave Web sites facing expensive legal fights for a single link to a site deemed to be “rogue.”

Instead, many companies have proposed an approach in which the Web sites could police themselves, overseen by an international nonprofit that tracks bad actors.

“This is an industry where you can start with a laptop and a good idea and make a billion-dollar company,” said Alexis Ohanian, the co-founder of Reddit.com. Ohanian said that if the new bill adds potential legal liabilities, the result could be less innovation on the Web.

Staff writers Paul Kane, Cecilia Kang, David Nakamura and Hayley Tsukayama contributed to this report.