00 UTC (10.30 am Sri Lanka time) protesting two proposed laws in the US which it says will "would seriously damage the free and open Internet" if implemented.
Reports said President Obama may veto both bills.
"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," Sue Gardner, Wikimedia Foundation Executive Director said in an online posting.
The proposed Stop Online Piracy Act (SOPA) in the U.
S. House of Representatives, and the PROTECT IP Act (PIPA) in the U.
S. Senate allows copyright holders to take action against internet infrastructure providers.
These include broadband providers, hosting companies, payment services and search engines to cut off websites accused of enabling or facilitating copyright infringement.
Sites with user generated content say the laws would also make it necessary constant monitoring and new restrictions.
There are concerns that such laws could also pave the way for oppressive states and rulers around the world to follow suit and further restrict the freedoms of their citizens.
The United States in recent years has led