Wired reports on documents obtained by security researcher Christopher Soghoian under a FOIA request, which show how federal law enforcement agencies have been tracking Americans -- in real time -- via credit cards, retail "loyalty program" cards, and rental car agencies.
More detail is at Soghoian's blog. He notes:
The document also reveals that DOJ's preferred method of obtaining this information is via an administrative subpoena. The only role that courts play in this process is in issuing non-disclosure orders to the banks, preventing them from telling their customers that the government has spied on their financial transactions. No Fourth Amendment analysis is conducted by judges when issuing such non-disclosure orders.
While Congress has required that the courts compile and publish detailed statistical reports on the degree to which law enforcement agencies engage in wiretapping, we currently have no idea how often law enforcement agencies engage in real-time surveillance of financial transactions.