One of Hillary Clinton’s most influential labor supporters has endorsed Sen. Bernie Sanders’ single payer healthcare plan.

Members from Service Employees International Union, which represents nearly 2 million healthcare and government workers, passed a resolution declaring medical care a human right at its national convention in May.

Obamacare, which the SEIU lobbied for and endorsed, failed to address inequality in the healthcare marketplace and insurance systems remain "confusing and inefficient." The union pledged to work to improve upon Obamacare with the goal of expanding into a government-run system.

"The American healthcare system allows the profit motives of providers, pharmaceutical companies, insurers, and other moneyed interests to leave us with unequal treatment access and poorer health outcomes at higher costs for consumers," the resolution says. "SEIU will support, defend and promote the Affordable Care Act and will work to improve it as a crucial step toward our ultimate goal of building a publicly-financed single-payer system that will recognize healthcare as a human right."

The human right extends beyond borders. The union plans to back measures, like one proposed in California, that would allow illegal immigrants to receive taxpayer-funded benefits.

"SEIU recognizes that our nations need healthcare systems with everybody included—regardless of immigration status—that includes the key priorities of affordability, universality, equity, equality, quality, participation, accountability, and transparency," the resolution says.

SEIU’s new healthcare stance mirrors that of insurgent socialist Sen. Bernie Sanders, rather than Clinton, whom the union endorsed in November. He has made universal healthcare a central theme in his campaign. He touts his belief in a Medicare-for-All system in each of his stump speeches. Clinton accused him in January of wanting to overturn Obamacare and dismantle Medicare—an attack Sanders dismissed as "nonsense."

"What a Medicare-for-all program does is finally provide in this country healthcare for every man, woman, and child as a right," he said. "We're not going to tear up the Affordable Care Act. I helped write it. But we are going to move on top of that to a Medicare-for-all system."

Healthcare could prove a major sticking point for Sanders supporters that the Clinton campaign will have to woo as she moves toward clinching the nomination. While the former secretary of state has moved to the left on economic issues, such as the minimum wage and free trade deals, she has not budged as much on healthcare reform. Mark Dudzic, national coordinator of the Labor Campaign for Single Payer, said that Clinton would be wise to follow SEIU’s lead.

"We’re hoping to challenge Secretary Clinton to embrace a more expansive view of healthcare justice, Dudzic told the Washington Free Beacon. "I think she’ll have a very tough Democratic convention if she doesn't talk about moving beyond the Affordable Care Act."

Dudzic said that SEIU’s endorsement signals an evolution on healthcare from labor groups, which have traditionally made healthcare benefits a selling point for membership. Several unions have criticized Obamacare for attempting to impose higher taxes on what are dubbed "Cadillac insurance plans."

Dudzic, a former labor leader, said that the current system is "unsustainable" as healthcare costs crowd out wage negotiations and other benefits.

"There’s a growing realization [among unions] that bargained healthcare is unsustainable. You look at that cost curve and people are looking beyond protecting the benefits they already have."

SEIU did not return request for comment.