"Heartbeat" singer Carrie Underwood is a Christian, but she is confusing a lot of evangelicals about her true faith given her support for same-sex marriage.

This is what members of the American Family Association (AFA) said after she was chosen to perform at the three-day Passion 2017 conference, which will take place at the Georgia Dome. The annual conference is hosted by Pastor Louie Giglio, founder of the Passion Movement and head of Passion City Church in Atlanta.

Every year, around 55,000 Christian youths from 90 countries and all 50 states in America gather to hear inspiring messages from Christian speakers and watch performances by well-known gospel singers, according to The Christian Post.

This year, Underwood made it to the list which included the likes of Chris Tomlin, Crowder, Matt Redman, Christy Nockels, Passion Band, and Hillsong UNITED. She performed her hit single "Something in the Water" on the first day of the conference.

AFA Executive Vice-President Ed Vitagliano said in a video posted on their website Monday that the decision to invite Underwood to sing before Christian youths was really questionable.

"The controversy is why would Louie Giglio put someone in front of millennials, who are struggling with this issue, who is basically saying that the Bible is not true in what it says about homosexuality," Vitagliano said, adding that there is a "growing strain within the evangelical community that is denying the truth of Scripture."

For his part, AFA General Counsel Abraham Hamilton III said a lot of churches and Christian leaders are making gay marriage confusing for the youth even though the Bible is clear that marriage should only be between one man and one woman.

"A lot of our church leaders find themselves pit between standing firm on God's Word, and remaining attractive to the masses," Hamilton said. "Popular stars like Carrie Underwood" aren't helping as well.

Meanwhile, AFA's s Outreach Director Wesley Wildmon wrote his displeasure about having Underwood as part of the Passion conference in an open letter for Giglio.

"God is right about marriage and Carrie Underwood is wrong," Wildmon said.

"I am writing to plead with you to consider the clarity of God's Word on marriage and reflect on it in the artist you choose for next year. It is God who has blessed you with this platform and it is God who can remove His hand of blessing if you become careless with His principles," he added.

Underwood revealed her support for gay marriage back in 2012. "As a married person myself, I don't know what it's like to be told I can't marry somebody I love, and want to marry. I can't imagine how that must feel. I definitely think we should all have the right to love, and love publicly, the people that we want to love," she told The Independent.