The Foreign Intelligence Surveillance Act (FISA), enacted by Congress after the abuses of the 1960s and 70s, regulates the government’s conduct of intelligence surveillance inside the United States. It generally requires the government to seek warrants before monitoring Americans’ communications. In 2001, however, President Bush authorized the National Security Agency to launch a warrantless wiretapping program, and in 2008 Congress ratified and expanded that program, giving the NSA almost unchecked power to monitor Americans’ international phone calls and emails. In February 2013, the Supreme Court dismissed the ACLU's lawsuit challenging the law.

https://www.aclu.org/cases/amnesty-v-clapper-challenge-fisa-amendments-act