Campbell says he doubts many would voluntarily choose to offer more money to the government than what is owed each year under current tax law. He noted attempts in states like Oklahoma and Massachusetts to encourage voluntary donations, which failed to generate any significant extra money.

"It exposes the hypocrisy in people who say this even though they don't do it," Campbell said.

Perhaps for that reason, he has not asked for an estimate of how much more federal revenue his bill would generate. "I have not asked for it to be scored," he said.

Campbell's bill is H.R. 1541, which is the same as the bill he introduced last year, H.R. 87.