OLYMPIA, Wash. — Washington Attorney General Bob Ferguson on Friday joined a multistate coalition suing over President Donald Trump’s decision to immediately halt federal payments to insurers under the national health care law.

“President Trump may not like the Affordable Care Act, but trying to sabotage it on the backs of hard-working Washingtonians is wrong – and illegal,” Ferguson said in a statement. The state is among nearly 20 states that has filed a lawsuit against the Trump administration.

At issue is a federal subsidy for deductibles and co-pays that helps lower costs for consumers with modest incomes. The White House says the government cannot legally continue to pay the so-called cost-sharing subsidies because they lack a formal authorization by Congress.

Consumers who qualify will still receive tax credits to help pay their silver premiums, however, millions of others across the country who buy individual health care policies without any financial assistance from the government and could face prohibitive increases.

The Congressional Budget Office estimated that premiums for a standard “silver” plan will increase by about 20 percent without the subsidies. In Washington state, the increase is expected to be between 9 and 27 percent, officials say.

Halting the payments would trigger a spike in premiums for next year, unless Trump reverses course or Congress authorizes the money.

“Continuing the federal funding that helps people buy health insurance is critical to maintaining a stable market in Washington,” Washington Insurance Commissioner Mike Kreidler said in a written statement. “This is not a bailout for insurance companies. It’s a lifeline for people who depend on affordable health insurance.”

A spokeswoman for Kreidler said that more than 330,000 people buy health insurance through the state’s individual market and more than 70,000 qualify for subsidies. However, 40,000 consumers who currently buy silver plans don’t get any financial assistance that would help offset a dramatic premium increase, said spokeswoman Stephanie Marquis.

“President Trump’s decision to stop making the cost-sharing reduction payments is nothing more than a deliberate and unconscionable sabotage of the personal health care of millions of Americans,” Gov. Jay Inslee said in a prepared statement. “It will directly harm middle-class families by hiking their premiums, deductibles and other out-of-pocket costs, while creating chaos and instability in the marketplace.”

The next open enrollment for the state exchange begins Nov. 1.