Shaun Dakin, founder of Citizens for Civil Discourse, said he thinks the calls should be regulated, the San Francisco Chronicle reports.

"We don't want an outright ban, but citizens have a right to privacy," Dakin said. "If someone wants to opt out, he should be allowed to do it."

Political calls were specifically exempted when the Federal Trade Commission set up a national Do Not Call list five years ago. Some states allow residents to opt out.

One of the more recent techniques is robocalls, using recordings of candidates or their better-known backers, including other politicians and movie stars.

"The calls are really an inexpensive way for an underdog candidate to let his message out to voters," Joshua Halpin, a spokesman for the American Association of Political Consultants, told the Chronicle. "This is a misguided attack on free speech which could lead us down a slippery slope to bans on direct mail, television ads and other types of political communication."