A Colorado couple has filed a lawsuit aimed at overturning the state's ban on same-sex marriage.

7News in Denver reports that Dr. Rebecca Brinkman and Margaret Burd applied for a marriage license from the Adams County Clerk's office. The clerk told them that they were not eligible because they are both female and offered them a civil unions license instead. The couple rejected the clerk's offer and instead filed suit in district court Wednesday.

Colorado legalized same-sex civil unions earlier this year, with the first couples being granted a civil union in May, but same-sex marriage was banned in the state in 2006. The lawsuit that Brinkman and Burd filed argues that civil unions do not grant the same rights to couples that marriage does.

In June, the U.S. Supreme Court ruled that Section 3 of the Defense of Marriage Act, the law that barred the federal government from recognizing same-sex marriages legalized by the states, is unconstitutional. The nation's highest court also overturned California's same-sex marriage ban, Proposition 8.

While neither of those rulings directly affect Colorado's law, 9News' legal analyst said that "it's simply a matter of time" before Colorado's same-sex marriage ban is also ruled unconstitutional.

Colorado House Speaker Mark Ferrandino (D-Denver), who became the state's first openly gay man to hold the title in the Legislature earlier in 2013, said after the DOMA ruling that LGBT-rights groups led by One Colorado are in the process of putting together a plan to repeal the ban on same-sex marriage in the state.

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  • New York

    New York lawmakers <a href="http://www.huffingtonpost.com/2011/07/24/new-york-gay-marriage_n_907901.html" target="_blank">legalized same-sex marriage on July 24, 2011</a>, making it the largest state at the time to pass such legislation.

  • Maryland

    Voters in Maryland <a href="http://www.huffingtonpost.com/2012/11/07/gay-marriage-victory_n_2085900.html" target="_blank">approved marriage equality in the November 2012 election</a>. Initially, the gay marriage bill was signed into law by Gov. Martin O'Malley (D) on March 1, 2012, but opponents gathered enough signatures to force the issue back onto the ballot. With the passing of marriage equality, same-sex marriage <a href="http://www.huffingtonpost.com/2012/12/31/maryland-gay-marriage_n_2389044.html" target="_blank">ceremonies began on Jan. 1, 2013</a>.

  • Connecticut

    Connecticut's Supreme Court <a href="http://www.huffingtonpost.com/2008/10/10/connecticut-gay-marriage_n_133605.html" target="_blank">ruled that same-sex couples had the right to marry on Nov. 12, 2008</a>, making it the third state in the nation to do achieve marriage equality.

  • Iowa

    Iowa's Supreme Court <a href="http://www.huffingtonpost.com/2009/04/03/iowa-gay-marriage-ban-rul_n_182782.html" target="_blank">ruled the state's gay marriage ban unconstitutional</a> on April 3, 2009.

  • Maine

    Maine <a href="http://www.huffingtonpost.com/2012/11/07/gay-marriage-victory_n_2085900.html" target="_blank">made history in the November 2012 election</a> when it became the first state to pass marriage equality on the ballot. Human Rights Campaign President Chad Griffin said, "Voters in Maine came to the common-sense conclusion that all people deserve the ability to make loving, lifelong commitments through marriage." Just three years ago, a popular vote overturned legislation that would have legalized same-sex marriage in the state.

  • Massachusetts

    Massachusetts became the first state in the nation to <a href="http://www.history.com/this-day-in-history/first-legal-same-sex-marriage-performed-in-massachusetts" target="_blank"> legalize same-sex marriage on May 17, 2004</a>. The state's Supreme Court initially found the ban on gay marriage unconstitutional on Nov. 18, 2003.

  • New Hampshire

    Same-sex couples were able to <a href="http://www.cbsnews.com/2100-201_162-6042937.html" target="_blank">begin seeking marriage licenses</a> on Jan. 1, 2010.

  • Vermont

    Vermont, which invented civil unions, became <a href="http://www.huffingtonpost.com/2009/04/07/vermont-legalizes-gay-mar_n_184034.html" target="_blank">the first state to legalize gay marriage through a legislature's vote</a> -- overriding the governor's veto. Same-sex couples were able to begin marrying on Sept, 1, 2009.

  • Washington D.C.

    Gay couples were able to <a href="http://www.huffingtonpost.com/2009/12/01/gay-marriage-dc-council-p_n_375435.html" target="_blank">begin marrying in the nation's capital</a> on March 9, 2010.

  • California

    The state initially began conducting gay marriages on June 16, 2008. On November 5, 2008, however, California <a href="http://www.huffingtonpost.com/2013/06/26/proposition-8-timeline_n_3503512.html" target="_blank">voters passed Proposition 8</a>, which amended the state's constitution to declare marriage as only between a man and a woman. On June 26, 2013, by a 5-4 vote, <a href="http://www.huffingtonpost.com/2013/06/26/hollingsworth-v-perry-ruling_n_3438269.html" target="_blank">the Supreme Court justices held in Hollingsworth v. Perry</a> that the traditional marriage activists who put Proposition 8 on California ballots in 2008 did not have the constitutional authority, or standing, to defend the law in federal courts after the state refused to appeal its loss at trial, opening the door for marriages to resume in the state.

  • Washington

    On February 13, 2012, Gov. Christine Gregoire (D) <a href="http://www.huffingtonpost.com/2012/02/13/washington-gay-marriage-signed-chris-gregoire_n_1273887.html" target="_blank">signed a law allowing same-sex marriage ceremonies</a> to begin on June 7, 2012. The process was delayed by gay marriage opponents who gathered enough signatures to put the issue up to a state vote in November 2012. <a href="http://www.huffingtonpost.com/2012/12/09/washington-gay-marriage-law_n_2266574.html" target="_blank">Gay marriage passed on November 7, 2012.</a> The official determination for Washington did not come until one day after the election because of the state's mail-in voting system.

  • Rhode Island

    Gay marriage came to Rhode Island when Governor Lincoln Chafee <a href="http://www.huffingtonpost.com/2013/08/01/gay-marriage-minnesota-rhode-island_n_3686034.html" target="_blank">signed the marriage equality bill</a> into law on May 2, 2013.

  • Delaware

    Delaware obtained gay marriage when <a href="http://www.huffingtonpost.com/2013/05/07/delaware-gay-marriage-law-_n_3232771.html" target="_blank">Governor Jack Markell signed the marriage equality bill it into law</a> on May 7, 2013.

  • Minnesota

    Minnesota same-sex couples achieved marriage equality when Gov. Mark Dayton signed the legislation into law <a href="http://www.huffingtonpost.com/2013/05/14/minnesota-gay-marriage-legal-_n_3275484.html" target="_blank">on May 14, 2013</a>.

  • New Jersey

    Newark Mayor Cory Booker <a href="http://www.huffingtonpost.com/2013/10/20/cory-booker-same-sex-marriage_n_4134116.html?&ir=Gay%20Voices&utm_hp_ref=gay-voices" target="_blank">began marrying same-sex couples</a> at City Hall at 12:01 a.m. on Oct. 21, 2013.

  • Hawaii

    Hawaii Gov. Neil Abercrombie signed same-sex marriage into law on Nov. 13, 2013, making it the 15th state to pass such legislation.

  • Illinois

    Illinois became the 16th state to legalize gay marriage, with the House <a href="http://www.huffingtonpost.com/2013/11/05/illinois-gay-marriage_n_4220793.html" target="_blank">having passed the bill on Nov. 5</a>. and Gov. Pat Quinn signing the legislation on Nov. 20.

  • New Mexico

    On Dec. 19, the New Mexico Supreme Court <a href="http://www.huffingtonpost.com/2013/12/19/new-mexico-gay-marriage_n_4474507.html?ir=Gay%20Voices" target="_blank">unanimously ruled</a> that same-sex marriage rights are protected under the Constitution.