A Christian ministry based in Utah is campaigning against the opening of a new Mormon temple in Carmel, Indiana.

Members of the Tri-Grace Ministries, whose main mission is "challenging the false doctrines of Mormonism," have set up a tent across the Church of Jesus Christ of Latter-Day Saints' Indianapolis Indiana Temple, which is about 23,000 sq. ft.

The organisation published a 12-page advertisement in community newspapers in Carmel, Westfield and Zionsville that campaigned against Mormon teachings, according to the Indy Star.

"This is our hope as we are doing the Indy temple outreach. We want Mormons to stop following Joseph Smith and start following Jesus!" the ministry posted on its Facebook page.

"In a sense, we believe they are not telling people the truth," according to Tri-Grace Ministries founder Chip Thompson. "They're not following what Jesus taught. It concerns us that Christians are being deceived by their message."

However, the anti-Mormon event has been branded as hate campaign against a minority religion.

"We don't treat people, who have been seriously picked on, in that way. We know better than that. We are better than that," said Chris Duckworth, pastor of the New Joy Lutheran Church in Westfield.

Duckworth found the Tri-Grace Ministries advertisement unappealing and an attack against Mormons.

"If my Mormon brother says he's a Christian, I'll accept his word at that. We might disagree in theology or have differences in opinion about what core tenets of Christianity are. But I'm not going to deny him the right to call himself what he or she in their faith believe they are," he told Indy Star.

The Indianapolis Indiana Temple has opened its doors for the public to see what's inside the temple starting on July 17 up to Aug. 8, ahead of the temple's dedication on Aug. 23.

The construction of the temple was announced by LDS President Thomas Monson in October 2010 and groundbreaking was held in September 2012.

It took three years before the temple was completed. It will serve about 30,000 Mormons in Indianapolis, South Bend, Lafayette, Muncie Fort Wayne, Bloomington and Champaign, Illinois.

"Latter-day Saint temples differ from the meetinghouses or chapels where members meet for Sunday worship services," according to an LDS statement.

It said, "Temples are considered 'houses of the Lord' where Christ's teachings are reaffirmed through marriage, baptism and other ordinances that unite families for eternity. Inside the temple, members learn more about the purpose of life and make covenants to serve God and their fellow man."

Thompson denied that their campaign is to attack Mormons. "We're just informing people," he said.