Sanders explained that while marriage is well-defined from state-to-state, what constitutes a domestic partnership or civil union often varies. In a handful of states, such as Illinois and Nevada, civil unions are considered the same as marriage.

"It probably would be a great advancement for equality and social justice if federal government recognized those unions as well," Sanders said.

For now, however, that's not the case.

The recent Supreme Court decision overturned Section 3 of the Defense of Marriage Act, which had prohibited the government from recognizing same-sex marriage for purposes of federal benefits programs. The 1996 law prevented same-sex spouses of federal workers from receiving coverage through their partners' plans.

The Obama administration, responding to the Supreme Court ruling, did go as far as making health, vision and dental benefits available to all same-sex spouses and children of legally married federal employees, even if they live in states where same-sex marriage is not yet recognized.

That means eligible same-sex couples living anywhere in the U.S. will qualify for federal-employee benefits as long as they possess marriage licenses from any of the 13 states that recognize same-sex marriage, as well as from the District of Columbia, which has also legalized such unions.

It remains unclear, however, how the Obama administration will treat same-sex couples and domestic partners outside the federal workforce, including on questions regarding Social Security, tax and veterans' benefits. The agencies that handle those programs have yet to issue guidelines on the subject.

"In those states that don't recognize same-sex marriage, this will absolutely bounce this issue back to the courts since it appears this may violate the equal protection clause," said Bruce Elliott, manager of compensation and benefits for the Society for Human Resource Management.