First, an anti-Christmas billboard was set up by the American Atheists outside a New Jersey entrance to the tunnel. It says: "You know it's a myth. This season, celebrate reason!"
The Catholic League countered with its own billboard near one of the tunnel's New York City entrances bearing the message, "You know it's real. This season, celebrate Jesus."
"There was a certain sense of exasperation" when the anti-Christmas billboard went up before Thanksgiving, said Bill Donohue, president of the Catholic League, which put up its response on Monday.
"We can't enjoy the Christmas season without someone trying to dumb it down or neuter it."
The atheist group picked its billboard site because of the high-profile location that would guarantee it was seen by a lot of drivers going by, said group President David Silverman.
"We wanted to get people who were sitting in traffic and had nothing to do but think about what they think and what they know," he said.
Silverman said the group hoped the billboard would gain attention, but was surprised by the Catholic group's response. He said he thought it was a kind of mockery, since it so closely followed the text of the atheists' sign.
"It's almost as if they're about to say, 'I know you are but what am I?"' he said.
Donohue said his group's billboard was not negative, and was actually a positive statement.
"We wanted to respond with a more positive statement as opposed to denigrating them," he said.
Silverman said the atheist billboard cost around $20,000. Donohue said his group's billboard was about $18,500. Both billboards will be up for at least the next couple of weeks.