"The highly organized and vocal movement for same-sex marriage, has begun the process of garnering equal rights for a small constituency in this country," Cindy Butler, executive director of Unmarried Equality, said in a statement.
"While we support the right of anyone who wants to to get married, this movement reinforces the idea that marriage is the only successful outcome for a relationship -- 47 percent of U.S. adults leading happily unmarried lives."
Almost invisible, unmarried people are treated unfairly in many areas of their lives paying higher rates for health and car insurance, they may be denied housing; they receive fewer employee benefits; and their Social Security balances revert to the federal system upon death. They are treated differently in issues related to child custody and adoption, Butler said.
Federal Law includes 1,138 mentions of the word marriage, showing how often marital status is used as a criterion for decision-making in the United States, Butler added.
People traveling alone have to pay more, single people pay more for smaller amounts of food and many discounts are offered to families only. In many ways, unmarried people subsidize the lives of legally married couples and families, Butler said.
In addition, unfair perceptions of unmarried life also persist -- unmarried men are often characterized as players or Peter Pans, while unmarried women are often characterized as undesirable or otherwise flawed.
Notable deaths of 2014 [PHOTOS]