A federal appeals court will review a ruling that struck down parts of Utah’s anti-polygamy law and was hailed as a landmark decision removing the threat of arrest for plural families in Utah.

The Utah’s attorney general’s office filed an appeal Thursday with the Denver-based 10th U.S. Circuit Court of Appeals, two weeks after it ended speculation by announcing it would challenge the ruling. The lawsuit was brought by the family on the TLC reality TV show “Sister Wives.”

In December, U.S. District Judge Clark Waddoups ruled in favor of reality show star Kody Brown and his four wives, saying a provision of the law forbidding cohabitation violated the family’s freedom of religion.

Waddoups’ ruling decriminalized polygamy, but bigamy — holding marriage licenses with multiple partners — is still illegal. If the ruling stands, Utah’s law would be identical to most other states that prohibit people from having multiple marriage licenses. In most polygamous families in Utah, the man is legally married to one woman but only “spiritually married” to the others.

Parker Douglas, chief of staff for Utah Attorney General Sean Reyes, said the state is appealing to ensure prosecutors aren’t hamstrung when they need to go after polygamous families where abuse may be occurring.

“The Browns don’t seem like the kind of situation that causes people too much pause,” Douglas said “But there are other situations where there are multiple spouse arrangements where there is abuse.”

Even though it’s been years since the anti-polygamy law was used in Utah, he said his office gets reports of abuse from polygamous families on a regular basis. He said several current investigations would be hampered if the ruling is upheld because it would become more difficult to prove a person has multiple spouses.

“When you have people who may be vulnerable, the state has a responsibility to make sure that its citizens are safe,” Douglas said.

The Brown family filed its lawsuit in July 2011 and fled Utah for Las Vegas last year under the threat of prosecution.

Brown family attorney Jonathan Turley wasn’t available for comment Thursday, but he previously said the family is prepared to take the legal fight to the U.S. Supreme Court if necessary. In a blog post last month after the state announced it would appeal, Turley argued that Utah should not challenge a ruling that reaffirmed freedom of religion and equal protection.

Polygamy is a legacy of the early teachings of the mainstream Mormon church, but the Salt Lake City-based Church of Jesus Christ of Latter-day Saints abandoned the practice in 1890 and strictly prohibits it today.

Briefings in the case will likely be done by December, Douglas said. He predicted oral arguments on the case would come next spring. The case is not on a fast track.