US Electronic Communications Privacy Act Title I (Wiretap Act, 18 USC 2510-2523) 2511(1)(a): 2511(1)(a) Do not intercept wire, oral or electronic communications

Unless the chapter specifically provides otherwise, no person may intentionally intercept, try to intercept, or procure anyone else to intercept or try to intercept, any wire, oral or electronic communication. For an employer this covers real-time capture of calls, email or messages in transit, keystroke or screen tools that acquire message contents as they are sent, and listening devices, unless an exception (provider, business extension, consent) applies.