SALT LAKE CITY — A federal judge ruled Friday that key parts of Utah’s polygamy laws are unconstitutional, handing a legal victory to a polygamist family that stars in the TLC reality show “Sister Wives.”

U.S. District Court Judge Clark Waddoups ruled that the phrase that forbids cohabitation with another person violates the First Amendment.

Kody Brown and his four wives filed their lawsuit in 2011 and fled to Las Vegas last year under the threat of prosecution.

Most states prohibit having multiple marriage licenses. Utah makes it illegal to even purport to be married to multiple partners or live together.