The couple share bank accounts, rent, utilities and grocery costs. She is the primary beneficiary on his life insurance policy. If something happens to him, she will split his retirement with his three grown children. Marriage seemed unnecessary. And Lewis never worried about legalizing the relationship.

But now, he wonders. The 51-year-old high school security director says he will vote against Amendment 3 - just in case. "I don't know that it would change my relationship. But the potential is there," Lewis says. "I guess that means I have a concern."

Lewis is one of 48,000 other Utahns classified as unmarried partners based on sampled data from the 2000 Census. Those couples are at the center of the legal and emotional arguments for and against the controversial marriage amendment. They include about 20,000 heterosexual unmarried couples and 4,000 gay couples - nearly 2,600 of whom have children.

Amendment opponents argue changing Utah's Constitution will hurt those families by throwing child custody, inheritance rights and medical decision-making power into question. But amendment supporters insist marriage and its inherent rights are sacred. They argue unmarried couples can sign legal contracts to gain some of the same rights. But opponents say even those private contracts could be challenged if the amendment passes.

Amendment 3 is written in two parts. The first sentence defines marriage as the legal union of a man and a woman. The second states "no other domestic union, however denominated, may be recognized as a marriage or given the same or substantially equivalent legal effect."

If the amendment passes, Utah's unmarried couples will be the guinea pigs to test the legal theories about its effect.

The thought worries AARP Associate State Director Laura Polacheck. Perhaps the most vulnerable group of unmarried Utahns who could be affected by the amendment are retirees. Retirees whose first spouses have died risk losing Social Security benefits and even pension payments if they remarry. Instead, many simply enter long-term relationships with other retirees. Older couples are at an age when such end-of-life rights inherent in marriage would come into play. The amendment might give children or other family members authority to challenge any agreements between unmarried partners.

The American Association of Retired Persons Utah has posted a caution about the amendment on its Web site. In Ohio, where a similar amendment is on the Nov. 2 ballot, AARP officially opposes the change.

"We want people to understand the ramifications," Polacheck said. "People should look at this very carefully. It would disrupt a lot of rights that couples have in terms of medical, legal and financial decisions. If a couple makes a decision to be committed to each other, but not to go through a marriage, they shouldn't suffer."

Besides questions about individual, unmarried couples, opponents of polygamy worry the amendment will make prosecution of polygamous couples more difficult. Tapestry Against Polygamy Director Vicky Prunty said she had doubts as soon as lawmakers balked at changing the amendment wording to "one man and one woman."

The questions of the anti-polygamy group also focus on the amendment's second paragraph. Prosecutors used Utah's Unsolemnized Marriage statute to try polygamist Tom Green for bigamy. Critics say the amendment throws that statute into question.

But former Juab County Attorney David Leavitt, who prosecuted Green, says those fears are silly.

"When Amendment 3 becomes part of the Utah Constitution, prosecution of polygamy will be easier, not harder," Leavitt said in a news release from Yes on 3, a coalition of amendment backers.

Amendment supporter Monte Stewart, who was appointed as a special prosecutor in the Green case, said polygamists back a larger campaign to legalize gay marriage.

"Polygamists want nothing more than legal approval of gay marriages and same-sex civil unions because that will open the door to legalized polygamy," Stewart said.

Don't Amend Alliance Director Scott McCoy says Stewart and Leavitt's assurances that nothing will change are not enough. The amendment's potential for cascading unintended consequences is too damaging for voters to risk changing the Utah Constitution.

"It's a mistake we're going to have to live with for a long time," McCoy said. "There's no gun to our head. A 'no' vote means the law in Utah stays exactly as it is now: gay marriages are banned, civil unions are banned, we won't recognize unions from other states. But we won't have some flawed amendment that nobody had the time to think about."

Legal arguments against Amendment 3

Part Two will throw into question existing "common-law" marriages and civil unions legalized in other states as well as jeopardizing the rights of couples in long-term, non-solemnized relationships and roommates who share economic interests. Private contracts establishing similar rights between unmarried couples also could be challenged.

The second clause prohibits future lawmakers from granting any rights inherent in heterosexual marriage - such as emergency medical decision-making, inheritance and hospital visitation - to unmarried heterosexual or gay couples. Utah's Cohabitant Abuse Act, which allows adults living together to file protective orders against their partners, could be impacted. And the amendment could make prosecution of polygamy more difficult.

Therefore, the amendment will disenfranchise gay citizens by blocking their access to the public process - a so-called unconstitutional "Bill of Attainder."

Amendment 3 could jeopardize domestic partner benefit packages provided by several Utah employers.

Legal arguments for Amendment 3

Part 2 only applies to those in sexual relationships.

Florida's Supreme Court decided that gay couples do not have a constitutional right to live a homosexual lifestyle and can be blocked from adopting foster children, to protect the "optimal family."

Amendment 3 does not block unmarried gay or heterosexual couples from signing legal contracts outlining medical decision-making power and inheritance rights. Visitation is an individual hospital's policy. Protective orders for cohabiting adults will not be affected by the amendment. Polygamy prosecution will only be easier if the amendment passes.

The Bill of Attainder doctrine is an antiquated and unconstitutional concept not accepted by any court.

Companies that offer domestic partner medical coverage have not stopped offering benefits in other states with similar marriage amendments already on the books.