A Washington political watchdog group has filed an ethics complaint with the Senate over robo-calls Sen. John McCain (R-AZ) made, urging voters to pressure their senators into supporting a McCain-led amendment to the Senate health care bill.

Citizens for Responsibility and Ethics in Washington, or CREW, filed the complaint with the Senate Ethics Committee on Wednesday, saying the Arizona senator and former presidential candidate violated Senate ethics rule 38, which prohibits senators from using political money to fund official Senate business.

CREW says when McCain used money from the National Republican Senatorial Committee to fund the robo-calls, he broke rule 38.

"By urging voters to call their senators to urge them to support his motion, Sen. McCain was engaged in grassroots lobbying," CREW said in a statement. "This activity clearly was related to Sen. McCain's official duties. By using an outside entity’s funds -- those of the NRSC -- to pay for expenses related to his official duties, Sen. McCain violated Senate rules."

McCain's robo-calls were targeted to five states represented in the Senate by conservative Democrats whose votes on the health care bill are seen as crucial. The robo-calls were targeted at senators Blanche Lincoln (D-AR), Michael Bennet (D-CO), Ben Nelson (D-NE), Byron Dorgan (D-ND) and Kent Conrad (D-ND), according to CREW.

In an interview with the Arizona Republic on Wednesday, McCain "laughed off CREW's complaint," describing the non-profit organization as "a far-left group."

"This is a political issue and we paid for it with political money," McCain said. "I mean, they might have a beef if I paid for it with Senate money or official money, but that was a political issue paid for with political contributions. It isn't any more complicated than that."

The Republic reported that "McCain speculated that Democratic health-care supporters and their allies are upset that the calls are resonating with voters."

"It might be an indication of how stung they are," the Republic quoted McCain as saying. "I'm told by the senatorial campaign committee that they are getting responses that they never have before. Our office, of course, is flooded with calls. We cannot keep up."

“The rules are clear. If Sen. McCain wanted to lobby voters in an effort to see his motion passed he should have paid for the calls himself," CREW executive director Melanie Sloan said in a statement. "Ethics rules are not optional; all the rules apply all the time, not just the ones senators like and not just when it is convenient to follow them.”