The Wisconsin-based atheist group, Freedom from Religion Foundation, warned public schools not to take their students to the Creation Museum or the Ark Encounter Park because of their “overtly religious atmosphere.”

CBN News reports that the FFRF sent over 1,000 letters to school districts across the country, many of them in Kentucky, warning them to stay away from these Christian attractions writing, “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.”

When the Ark Encounter founder Ken Ham heard about the FFRF’s letters, he decided to challenge them, noting that he would not stand for their “bullying and intimidation.”

Ham offered free admission to all public-school teachers and students that come for “official public school trips.”

He told Fox News, “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 continued, “I would like to see some public schools and public parks stand up to them and not succumb to their bullying and intimidation.”

“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,” he proclaimed.

Ham has also assured schools that he has “expert attorneys who are willing to defend them” if the FFRF tries to sue them for a first amendment violation.

Franklin Graham backed Ham in a Facebook post on Sunday saying, “Noah wasn’t intimidated by atheists in his day, and neither is the builder of the Ark Encounter in Kentucky, Ken Ham.”