The 15 states led by the office of Republican Kansas attorney-general Kris Kobach say a rule adopted by the US health and human services department in May violates a federal law that prohibits giving public benefits to people who lack legal immigration status.

The rule classifies participants in the Deferred Action for Childhood Arrivals (DACA) programme created in 2012 as “legally present” in the US, allowing them to enrol in basic healthcare programmes created by the 2010 Affordable Care Act, known as Obamacare.

But Kansas and the other states in their lawsuit said that because individuals have to lack legal status to enrol in DACA, they are by definition not legally present in the country.

They said the rule improperly encourages DACA recipients to remain in the US illegally, in turn forcing states to spend millions of dollars on public services for them and their children.

The White House and the health and human services department did not immediately respond to requests for comment.

Separately on Thursday, Texas governor Greg Abbott, a Republican, issued an executive order directing state officials to begin tracking the costs to the state of providing medical care to people in the country illegally.

The DACA programme offers deportation relief and work permits to “Dreamer” immigrants who were illegally brought to the US and overstayed a visa as children. About 530,000 people are currently enrolled in the programme, which remains subject to an ongoing legal fight.

Under the HHS rule, which takes effect Nov 1, DACA enrolees will have access to insurance and related financial assistance such as tax credits and reduced out-of-pocket costs under the change.

Immigration has emerged as a top issue for voters ahead of the Nov 5 presidential election pitting vice-president Kamala Harris, a Democrat, against Republican former president Donald Trump.

Trump, an immigration hardliner, tried to end DACA during his presidency but was denied by the US Supreme Court. The Trump campaign in May blasted the healthcare rule, calling it “unfair and unsustainable.”