A Wisconsin-based atheist group has taken aim at the Ark Encounter tourist attraction in Williamstown, Kentucky by sending a letter to more than 1,000 school districts in five states, warning them that a field trip to the Ark would be unconstitutional.

The Freedom From Religion Foundation wrote: "Public schools cannot organize trips for students to either the Creation Museum or the Ark Park. It is unacceptable to expose a captive audience of impressionable students to the overtly religious atmosphere of (Ken) Ham's Christian theme parks."

Back in August, the group known as American Atheists mailed similar letters to schools in Kentucky.

Ken Ham, the Ark Encounter's founder, said the atheist groups are merely trying to bully and intimidate kids while continuing their attacks against Christians.

"The atheist groups like American Atheists and the Freedom From Religion Foundation have been increasingly aggressive to restrict the free exercise of religion — particularly Christianity — and they've tried to brainwash people with an interpretation of the First Amendment...it does not mean that Christians are second class citizens," he told Fox News.

Ham explained that all school officials have to do is to tell their kids that their visit is intended to be merely educational. Students do not have to believe what they see, much like visiting a mosque.

"I would like to see some public schools and public parks to stand up to them and not succumb to their bullying and intimidation," Ham said. "Because the FFRF has sent letters to 1,000 school districts, I'm offering them free admission for the teachers, students who come on an official public school trip."

"And if they do sue them, we have expert attorneys who are willing to defend them in court and I'd like to see a test case go to the Supreme Court and stop this nonsense from these atheist groups who try to outlaw Christian influence in this nation," he added.

Faith leaders like evangelist Franklin Graham have come out in support of Ham and his efforts.

On Saturday, Graham posted to his Facebook page about the incident, writing: "Noah wasn't intimidated by atheists in his day, and neither is the builder of the Ark Encounter in Kentucky, Ken Ham. The liberal, atheist Freedom From Religion Foundation sent letters to 1,000 school districts in 5 states, threatening them that they could not bring students to the Ark Encounter on field trips because it was unconstitutional. The American Atheist group had also sent letters to Kentucky schools. Ken is right, these godless, hyper-secular groups have "tried to brainwash people with an interpretation of the First Amendment." I really like Ken's response! He's offering all of those school districts FREE ADMISSION to students and teachers who come on public school field trips! I hope every school takes him up on the offer. What an opportunity! There's no question it's educational and filled with #truth. Comment below to let Ken Ham and everyone at the Ark Encounter know that you will pray for them to stand strong and continue their great work."