A case before the Supreme Court challenging the liability shield protecting websites such as YouTube and Facebook could "upend the internet," resulting in both widespread censorship and a proliferation of offensive content, Google said in a court filing Thursday.

In a new brief filed with the high court, Google said that scaling back liability protections could lead internet giants to block more potentially offensive content—including controversial political speech—while also leading smaller websites to drop their filters to avoid liability that can arise from efforts to screen content.