Lawyers for Foursquare, Kickstarter, Meetup, and Tumblr said on Monday that they were seeking to join the clash on Facebook's side. The New York Civil Liberties Union and the American Civil Liberties Union also have recently said they were backing Facebook.
They see the warrants - for data including friend lists, photos, and private messages, many of them from users who have yet to be charged and may never be - as a troubling message for digital-age privacy. Facebook has said it had previously never received so many search warrants.
''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's now in private practice and representing the four tech companies, all New York-based.
A judge has said the search warrants were justified. So do Manhattan prosecutors, who sought the data for a sweeping disabilities-benefit fraud investigation. Some 134 people have been charged so far, more than half have pleaded guilty, and prosecutors have said more could be implicated.
''Prosecutors have a right and a responsibility to collect evidence in criminal cases, wherever that information is stored,'' Joan Vollero, spokeswoman for the Manhattan district attorney's office, said Monday.
A Manhattan judge approved the 381 warrants in July 2013, saying law enforcement has authority to search massive amounts of material to seek evidence. The case was secret until it was unsealed and Facebook disclosed it in June.
The Menlo Park, California-based company has turned over the information but is appealing the court order that required it to do so.
The case involves police and fire retirees, allegedly instructed to claim they were too psychologically devastated to work. Instead, they led robust lives - some flew helicopters, traveled overseas, did martial arts, went fishing - and sometimes aired the alleged proof of their active lives on Facebook, prosecutors say.
Prosecutors have said they gave the judge 93 pages of details on why all the accounts were targeted.
But Facebook has said prosecutors cast too wide a net. Their campaign amounted to the online equivalent of searching ''an entire neighborhood of nearly 400 homes,'' the company said in a June court filing. The users ranged from high school students to grandparents, Facebook said.
Over the years, online companies have sometimes won, sometimes lost, in battling authorities' demands for user information.