"An advocacy ad, with a number to call Congress, is something we try to stay away from," he added.

Many such systems have less stringent policies against advocacy ads.

Mr. Case finds great glee in showing his recent advocacy ads, many of them with a surprising twist.

"With a mainstream audience, you have to be pretty clear, especially with advocacy ads," Ms. Murphy added.

"They've got a clever agency and a modest budget, like Kenneth Cole with his advocacy ads," he said.

"These are straight advocacy ads that talk about excise tax increases and black market cigarettes and other ramifications of the McCain bill."

As other advocates have butted up against similar policies prohibiting advocacy ads at most national television channels, they have increasingly resorted to making local buys.

"How could you take an advocacy ad and have it reflect the values of the entire nation?"

Even before the start of the campaign period, candidates had begun releasing infomercials without explicitly stating that voters should vote for them; instead these were called "advocacy ads".

Nor is it compelled to run advocacy ads at all.