(RNS) Humanists went to federal court in Denver to prevent Colorado schoolchildren from being asked to put together Christmas gift boxes sponsored by an evangelical charity.

The hearing on Wednesday (Nov. 16) was the result of a suit filed by the American Humanist Association, a national organization of humanists, atheists and freethinkers. They are representing three humanist families who say the constitution's guarantee of the separation of church and state is violated when their suburban Denver school district asks their children to assemble Christmas gift boxes that include the "opportunity . . . to faithfully follow Jesus Christ."

The boxes are a project of Operation Christmas Child, a branch of Samaritan's Purse, the charity run by Franklin Graham, an evangelical minister and son of the Rev. Billy Graham. Its mission is “to follow the example of Christ by helping those in need and proclaiming the hope of the Gospel.”

The humanist association alleges the Douglas County School District, located in south suburban Denver, also participated in a Fellowship of Christian Athletes mission trip to Guatemala and Adventures in Missions, an organization that says it "emphasize(s) prayer and relationships in our work amongst the poor."

"This is not like a soup kitchen where, even if it is run through a church, there is no proselytizing," said Monica Miller, legal counsel for AHA's Appignani Humanist Legal Center. "Operation Christmas Child puts religious tracts in the boxes after they are assembled and the school district may not align itself with any religious organization."

An Operation Christmas Child spokesperson said it does not determine who does or does not participate in its annual gift box program and has collected over 135 million show box gifts to date.

This is not the first time Operation Christmas Child and the American Humanist Association have tussled. In 2013, the humanist group sent "letters of warning" to school districts in Colorado and South Carolina where Operation Christmas Child was invited into public classrooms.

The South Carolina school cut its tied with Operation Christmas Child, but the Colorado school did not. The proceeding in the Tenth Circuit Court of Appeals stems from that initial incident.