According to the Huffington Post:
Sen. John McCain (R-Ariz.) broke Senate rules when he recorded a robocall touting his amendment to the health care bill, according to a complaint filed with the Senate Ethics Committee by watchdog group Citizens for Responsibility and Ethics in Washington.
The National Republican Senatorial Committee paid for the call, which targeted the constituents of swing senators in five states and attacked the current health care reform bill for "cutting $500 billion in vital Medicare coverage for our seniors." The call urged constituents to sign a petition encouraging the senators to support McCain's amendment.
In its complaint, CREW cites Senate Rule 38, which prohibits senators from using private donations to support official Senate activities.
Interested in hearing the actual audio? This site has a copy of the voice mail for you to hear: