Lawyers for a family made famous by the TV show "Sister Wives" are set to ask a federal appeals court on Thursday to uphold a ruling that decriminalized polygamy in Utah.

The case is scheduled to come before the 10th Circuit Court of Appeals in Denver after the Utah Attorney General appealed the ruling that struck down key parts of the state law banning polygamy.

State attorneys say they don't plan to charge plaintiff Kody Brown and his four wives if the law stands, but it should stay on the books because it helps curb abuses like underage marriage.

The Brown family says their reality show "Sister Wives" shows polygamous unions can be as healthy as monogamous ones. They argue that making marriages like theirs a crime violates the right to privacy and freedom of religion.

The family won a legal victory in 2013, when U.S. District Judge Clark Waddoups found that a key part of Utah's bigamy law forbidding cohabitation violated the Brown's right to religious freedom and struck it down. Bigamy, or holding multiple marriage licenses, is still illegal.

The decision was hailed as a landmark case that removed the threat of arrest for plural families, but Utah said that it could weaken their ability to go after polygamists like jailed leader Warren Jeffs.

Prosecutors pointed to Jeffs, who is in prison after being convicted of assaulting underage girls he considered wives, as evidence that the practice can be associated with crimes such as sexual assault, statutory rape and exploitation of government benefits. Even though Utah has a longstanding policy against prosecuting otherwise law-abiding adults in polygamous marriages, prosecutors say outlawing the practice helps investigators gather evidence and strengthens cases against other abusers.

The Browns counter that there are other laws on the books against those crimes, and banning the practice can sow distrust of authority.

Their attorney Jonathan Turley has also pointed to the landmark U.S. Supreme Court ruling legalizing same-sex marriage, saying it shows laws restricting consensual adult relationships are outdated even if certain unions are unpopular.

There are about 30,000 polygamists in Utah, according to court documents. They believe polygamy brings exaltation in heaven — a legacy of the early Mormon church. The mainstream Salt Lake City-based Church of Jesus Christ of Latter-day Saints abandoned the practice in 1890 and strictly prohibits it today.