WASHINGTON — The Department of Veterans Affairs must reimburse veterans for emergency medical care at non-VA facilities, a federal appeals court ruled Monday — a decision that could be worth billions of dollars to veterans.

The U.S. Court of Appeals for Veterans Claims said the VA has been wrongfully denying reimbursement to veterans who sought emergency medical care at non-VA facilities, and struck down an internal VA regulation that blocked those payments.

"All of this is unacceptable," said the ruling, which ordered the VA secretary to "readjudicate these reimbursement claims."

Plaintiffs' lawyers say that based on past estimates by the VA, the department is now on the hook for between $1.8 billion and $6.5 billion in reimbursements to hundreds of thousands of veterans who have filed or will file claims between 2016 and 2025.

Former Coast Guardsman Amanda Wolfe, one of the plaintiffs in the case, told NBC News on Tuesday, "I’m just overjoyed. I think it means change, it means that veterans don’t have to be afraid of receiving care, emergency care. They can have that sense of security that sense of peace knowing they are covered if they have emergency care."

“I served side by side with some of these veterans who were impacted and to think that this is going to make a difference for them is what is most important to me."

The VA told NBC News in a statement that the department, “is aware of this decision and reviewing it.”

In 2015, the court struck down a previous version of the internal VA regulation that refused any coverage for an emergency claim when another form of insurance covered even a small part of the bill. The court said the regulation violated a 2010 federal law.

Monday's ruling found the department had violated the same federal law with its revision of the reimbursement regulation. The panel saidthe new rule, issued in January 2018, actually created another obstacle for veterans by forbidding the VA from reimbursing medical expenses for emergency services at non-VA facilities.

Hard-won victory

In September 2016, Wolfe went to the emergency room because her appendix was about to burst. After a speedy recovery, she figured she was all set — she had two kinds of insurance, a private plan she paid for and her Veterans Affairs benefits.

Her private insurance covered most of the more than $20,000 bill for her hospital stay. But six months later, the VA denied her claim for the roughly $2,500 that remained, putting her in an unexpected financial bind. She paid off the bill in 2017, but had been fighting for reimbursement ever since. This year, her case made it all the way to the Court of Appeals for Veterans Claims.

When the VA's Inspector General released a report in August revealing major problems in the way the VA reimburses veterans for emergency care at non-VA facilities, Wolfe was shocked to learn how many other veterans were in unnecessary binds just like hers.

The August report found that in just one recent six-month period, the VA left roughly 17,400 veterans to pay out-of-pocket for $53 million in emergency medical treatment the government should have covered.

"The Court’s decision rights a terrible injustice and its order ensures that veterans who were unjustly denied reimbursement for critical emergency treatment at non-VA facilities will finally be reimbursed," said Bart Stichman, executive director of the National Veterans Legal Services Program, which represented Wolfe in the case. “It is a hard-won victory for hundreds of thousands of veterans."

Wolfe's lawsuit is only the second case the Court of Appeals for Veterans Claims has ever granted class action status. The first was earlier this year.