Thousands of American nonbelievers are gathering for weekly Sunday Assembly meetings that both supporters and detractors call “atheist megachurches.”

The founders of the movement, which started earlier this year in Great Britain, are introducing the gatherings in cities across the U.S. as part of the group’s “40 Dates, 40 Nights” tour.

British comedians Sanderson Jones and Pippa Evans, who founded the Sunday Assembly to gather like-minded nonbelievers in a congregation-like setting, say their movement is not intended to be a joke.

The meetings have been drawing several hundred men, women and children for music performances, inspirational talks and quiet reflection in cities such as San Diego, Nashville and New York.

The group’s motto is Live Better, Help Often, Wonder More.

Evans and Jones are hoping the tour, which also includes meetings in Australia, will raise $800,000 to help launch more atheist congregations around the world, and so far they’ve raised $50,000.

Recent polls show a growing number of Americans claim no religious affiliation, which can include those who believe in God but lack formal ties to organized religion.

But some atheists say an organized movement runs counter to the point of nonbelief.

"The idea that you're building an entire organization based on what you don't believe, to me, sounds like an offense against sensibility," said Michael Luciano, a self-described atheist who was raised Roman Catholic. "There's something not OK with appropriating all of this religious language, imagery and ritual for atheism.”