Amendment XIV - Citizenship rights.

1. All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. - The US Constitution

Montana High Court Says University System Must Provide Gay Employees with Domestic Partner Benefits

...the Montana Supreme Court ruled today that the state must provide lesbian and gay employees of the University of Montana System with the option of purchasing health insurance and other employee benefits for their domestic partners.

The court, in a four-to-three decision, ruled that the University System's policy of excluding lesbian and gay employees from equal employment benefits violates the state constitution's equal protection guarantees.

The legal precedent now exists to enforce the US Constitution's equal protection clause on behalf of same-gender couples across the country and overturn both federal and state "Defense of Marriage" laws.