Internet heavyweights Facebook, Google, Twitter and Yahoo! joined ranks Tuesday to oppose legislation in the US Congress designed to crack down on online piracy.

In a joint letter, the firms said they "support the bills' stated goals -- providing additional enforcement tools to combat foreign 'rogue' websites that are dedicated to copyright infringement or counterfeiting."

"Unfortunately, the bills as drafted would expose law-abiding US Internet and technology companies to new uncertain liabilities, private rights of action, and technology mandates that would require monitoring of websites," they said in the letter to the House and Senate judiciary committees.

"We are concerned that these measures pose a serious risk to our industry's continued track record of innovation and job-creation, as well as to our nation's cybersecurity," they said.

The legislation introduced in the House and Senate would give US authorities more tools to crack down on "rogue" websites accused of piracy of movies, television shows and music and the sale of counterfeit goods.

The bills have received the backing of Hollywood and the music industry but have come under fire from digital rights and free speech groups.

In the letter, the Internet companies said "we cannot support these bills as written and ask that you consider more targeted ways to combat foreign 'rogue' websites dedicated to copyright infringement and trademark counterfeiting."

The House Judiciary Committee is to hold a hearing on the bill on Wednesday.

The Obama administration has come in for some criticism for shutting down dozens of "rogue websites" over the past year as part of a crackdown known as "Operation in Our Sites."

US authorities in November, for example, shut down 82 websites selling mostly Chinese-made counterfeit goods, including golf clubs, Walt Disney movies, handbags and other items.

In addition to Facebook, Google, Twitter and Yahoo!, the other companies signing the letter were eBay, LinkedIn, Mozilla and Zynga.