Google and Mozilla have joined the raft of companies opposing the Stop Online Piracy Act (Sopa) and the PROTECT IP Act (Pipa) in the US.
Various tech giants have criticised aspects of the two bills, Pipa going through the US Senate and Sopa in the House of Representatives.
Wikipedia and Wordpress have both shutdown for the day in protest, whilst other firms such as Rackspace and Twitter have voiced their opposition to Sopa and Pipa.
We oppose these bills because there are smart, targeted ways to shut down foreign rogue websites.
Google claimed the acts would censor the web, handing powers to law enforcement to filter the web and block access to tools that would bypass such filters.
"We know from experience that these powers are on the wish list of oppressive regimes throughout the world," said David Drummond, Google's senior vice president for corporate development and chief legal officer, in a blog post.
"Sopa and Pipa also eliminate due process. They provide incentives for American companies to shut down, block access to and stop servicing US and foreign websites that copyright and trademark owners allege are illegal without any due process or ability of a wrongfully targeted website to seek restitution."
Google also claimed the acts would not stop piracy, as pirate sites would simply change their addresses.
The internet giant has highlighted this issue on its US home page and is asking people to petition congress via a special landing page.
"Like many businesses, entrepreneurs and web users, we oppose these bills because there are smart, targeted ways to shut down foreign rogue websites without asking American companies to censor the internet," a Google spokesperson said.
Mozilla has chosen to redirect traffic from Mozilla.org to an action page for 12 hours. Visitors will be presented black page with a call to action message to increase awareness of Pipa and Sopa.
The action will run from 13:00GMT today through to 01:00 GMT tomorrow.
"While we generally support the end goal of the legislation to limit online piracy of legitimate content we believe that both Pipa and Sopa, in their current drafts, have serious flaws in the proposed implementation of the legislation," said Gary Kovacs, CEO of Mozilla, in a blog post.
"Among them is the requirement for online service and content providers to police the system. This would create an undue burden on businesses that were not designed for this purpose, would require more lawyers to be involved, and would extend the hand of government much deeper into these organisations."
Kovacs claimed the acts would "spread a chilling effect across the web that would significantly limit innovation."
Sopa has been shelved for the time being, but Pipa could still pass through the Senate.
The Wikipedia blackout is not as comprehensive as the company may have liked. Firefox users can simply add the NoScript add on and disable JavaScript to access the site.
