An anonymous reader writes: When encrypted email provider Lavabit shut down in August, it was because U.S. authorities demanded the company release encryption keys to get access to certain accounts. Lavabit's founder, Ladar Levison, is facing contempt of court charges for his refusal to acquiesce to their demands. But now the ACLU has filed a 'friend of the court' brief (PDF) in support of Levison, saying that the government's demand 'fatally undermined' the secure email service. 'Lavabit's business was predicated on offering a secure email service, and no company could possible tell its clients that it offers a secure service if its keys have been handed over to the government.' The ACLU added, 'The district court's contempt holding should be reversed, because the underlying orders requiring Lavabit to disclose its private keys imposed an unreasonable burden on the company. Although innocent third parties have a duty to assist law enforcement agents in their investigations, they also have a right not to be compelled "to render assistance without limitation regardless of the burden involved."' Lavabit is also defending itself by claiming a violation of the 4th amendment has occurred.