Facebook's fight against prosecutors over nearly 400 search warrants for users' postings is drawing support from other social media companies.
Foursquare, Kickstarter, Meetup and Tumblr are keen to join the clash on Facebook's side.
They see the warrants - for data including friend lists, photos and private messages - as a troubling message for digital-age privacy.
"With the burgeoning tech industry in New York, the need to protect the privacy of users has never been greater," said Richard Holwell, a former federal judge who is now in private practice and representing the four tech companies.
A judge has said the warrants were justified, as do Manhattan prosecutors who sought the data for a sweeping disabilities-benefit fraud investigation.
Some 134 people have been charged so far and prosecutors have said more could be implicated.
"Prosecutors have a right to collect evidence in criminal cases, wherever that information is stored," said Joan Vollero, spokeswoman for the Manhattan district attorney's office.
A Manhattan judge approved the 381 warrants in July last year, saying law enforcement has authority to search massive amounts of material to seek evidence.
Online companies have sometimes won, sometimes lost, in battling authorities' demands for user information.