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NEW YORK -- When you go on the Internet today, you may notice several popular websites have gone dark. That's because they're taking on the fight against legislation pending in Congress that's aimed at shutting down sites that share pirated movies and other content.

Among the websites are Reddit, Craigslist and Wikipedia. Google has also blacked out the logo on its home page.

Wikipedia's English language site is shut down for the day in protest.

Visitors to the site see a black and white page with the message "Imagine a world without free knowledge."

The Stop Online Piracy Act, or SOPA, aims to crack down on copyright infringement by restricting access to sites that fuel it.

If SOPA passed, copyright holders would be able to complain to law enforcement officials and get websites shut down.

Opponents say that could lead to Americans losing access to thousands of sites across the web.

Below is a Storify item created by author and professor Andrew Lih about the blackout.