About 900 sites have blacked out in protest of the Cyber Intelligence Sharing and Protection Act, or CISPA, which passed a House vote last week.
The protest is being led by the hacker activist group Anonymous.
The bill seeks to remove current restrictions on websites that prevent them from mining and sharing sensitive information about their users.
Various privacy groups strongly oppose the bill, as does President Barack Obama, who said he would veto it in its current form.
Certain subsections of Reddit have joined the cyber protest, the Reddit itself has not taken part.
Reddit General Manager Erik Martin said, "We've been running ads against CISPA for the past few months, but we didn't think the timing was right for us to participate in today's blackout."
Martin said that he is "going to plan more action closer to the vote in the Senate."