Police must get warrants to access Americans' e-mail and track their cell phones, according to new privacy legislation that promises to spark a political spat between high-tech firms and law enforcement.

The bill, introduced today by Rep. Zoe Lofgren -- a Democrat who represents the heart of Silicon Valley, including the home turf of Apple, Google, and Intel -- would generally require law enforcement officials to obtain a search warrant signed by a judge before they can access cloud data or location information.