The Freedom from Religion Foundation (FFRF) sent a letter to the superintendent of the Indian Creek School District, stating that is was "unconstitutional" for the district to allow the Bible study to be offered during school hours at Indian Creek Middle School.
The group also flagged the potential dangers of Bobbyjon Bauman from the Valley Youth Network being involved with students aged 11-14 years-old.
"It is unconstitutional for the district to offer religious leaders access to befriend and proselytise students during the school day on school property," FFRF wrote.
"This predatory conduct is inappropriate and should raise many red flags. The district cannot allow its schools to be used as recruiting grounds for churches during the school day."
The Church-State separation group became aware of the voluntary Bible study after the pastor shared a Facebook post about how many students attended.
Mr Bauman shared a post saying: "I shared the gospel with them using Romans 6:23 as the touchstone verse. None of the kids in any of the four Bible study groups even knew what the word 'gospel' meant, so I was able to share with them the significance of the life, death and resurrection of Jesus Christ.
"The kids were very responsive to the message and we had 30 of them request Bibles because they didn't own one, so next week, we will be bringing them Bibles."
It is not known if the Indian Creek School District plans to respond.
FFRF recently challenged the state of Ohio for allowing Biblically-themed murals on a municipal building.
The mural includes artwork of an eagle with the words "Under His Wings Shall You Find Refuge Psalm 91".
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