Until now, Google and Facebook—which have been staunch supporters of net neutrality in the past—have stayed out of the debate. But this week, they confirmed they will join other companies in telling consumers to oppose the FCC’s plan to tear up the current rules.

The participation of Google and Facebook in the day-of-action campaign could be a game-changer because their sites are visited by hundreds of millions of Americans, and a message from them could rally new opposition to the FCC plan.

The two tech giants have yet to explain what specific actions—such as displaying a banner on their homepage—they will take. In emails to Fortune, spokespeople for Facebook and Google confirmed the companies will participate but declined to provide additional details.

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The news from Facebook and Google comes a month after Amazon, in a surprise move, became the first big tech firm to join the likes of Reddit and Etsy in signing onto the day of action. Soon after Netflix likewise announced it would participate.

The July 12 campaign is reminiscent of another day in 2012 when the tech industry rebelled against a controversial copyright bill known as SOPA by altering or even blacking out their websites. The resulting uproar resulted in Congress withdrawing the bill.

It’s unclear though if next week’s campaign, organized by a group called Fight for the Future, will do much to sway the FCC’s proposal to revoke net neutrality. While the agency is accepting public comments on the plan, its current chairman, Ajit Pai, is a former Verizon lawyer and a staunch ideologue who regards the current rules as a burden on business—and he has the votes to push through the revocation measure.

A popular outcry, however, could lead Congress or the White House to put pressure on Pai to reconsider his plan to end net neutrality.

The current comment period lasts until July 17, and will be followed by a second round that extends into August.