Ben Lee, Twitter's legal counsel, said in an email statement that the company's terms of service make "absolutely clear" that users own their content. "Our filing with the court reaffirms our steadfast commitment to defending those rights for our users," he said.

The legal fight is being monitored for its potential impacts. Aden Fine, a senior staff attorney with the American Civil Liberties Union, wrote that Twitter should be applauded for standing up for Harris since internet companies represent an important line of defense for users' free speech rights.

"This is a big deal," Fine wrote. "Law enforcement agencies -- both the federal government and state and city entities -- are becoming increasingly aggressive in their attempts to obtain information about what people are doing on the Internet."