Anthony Gonzales and Mark Johnson met in 1998 and spent the next 15 years together. When New Mexico legalized same-sex marriage in 2013, they married the very next day. Six months later, however, Johnson passed away from cancer.

Despite living together as a committed couple for over a decade and marrying as soon as they were legally permitted, Gonzales was not eligible to receive his husband’s Social Security benefits. This is because Section 216 of the Social Security Act stipulates that couples must be married for at least nine months in order for the surviving spouse to receive benefits.

Anthony Gonzales, from right, and his late husband, Mark Johnson, in 1998. Michael Kaplan

“We established a joint checking account, named each other as our beneficiaries, and cared for each other when sick — basically, all the things that committed couples do,” Gonzales said in a statement shared with NBC News. “We got married as soon as humanly possible, but I’m still barred from receiving the same benefits as other widowers, even though my husband worked hard and paid into the social security system with every paycheck.”

As a result, LGBTQ civil rights group Lambda Legal announced on Thursday that it is suing the Social Security Administration on Gonzales’s behalf.

“Same-sex couples who weren’t able to marry for most of their relationship faced discrimination throughout their lives, and now surviving spouses like Anthony face it all over again, after their loved one has died,” Lambda Legal attorney Peter Renn said in a statement. "These benefits are as essential to the financial security of surviving same-sex spouses in their retirement years as they are to heterosexual surviving spouses.”

Over the past three months, Lambda Legal has filed lawsuits against the Social Security Administration on behalf of three LGBTQ people, including Gonzales, whose spouses passed away before nine months of marriage. The other cases involve 63-year-old lesbian Helen Thornton, whose partner died before Washington state started permitting same-sex couples to marry, and 65-year-old Michael Ely, whose partner of 43 years died seven months after Arizona legalized gay marriage.

Renn called the withholding of Social Security benefits “cruel” and said all three cases underscore “the ongoing harm that a number of same-sex couples continue to experience from marriage bans, despite those laws having been struck down.”

“The U.S. Supreme Court has held that the government may not exclude same-sex couples from marriage, or deprive them of benefits associated with marriage, but the federal government continues to discriminate against same-sex couples today, based on their unconstitutional exclusion from marriage in the past,” the latest suit states.

The Social Security Administration did not respond to NBC News’ request for comment on this story.

Anthony Gonzales, from right, and his late husband, Mark Johnson. Anna Reichbach

Renn said he is optimistic about the case’s success because “the law is on our side.” He said the government has until February 11 to respond to Lambda Legal’s motion, and he expects the court to rule on the case in the spring.

He called these cases an “unfinished chapter of marriage equality” and a question of allowing same-sex couples to realize all the rights granted by the Supreme Court’s 2015 Obergefell v. Hodges decision.

“The truth is there are still people suffering as a result of yesterday’s discrimination,” Renn added.

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