OLYMPIA, Wash. — Washington Attorney General Bob Ferguson announced Tuesday that his office has sued a Tacoma hospital over allegations that it illegally withheld charity care from tens of thousands of low-income patients.

The lawsuit against St. Joseph Medical Center was filed in Pierce County Superior Court. Ferguson said that the hospital has been violating the state’s consumer protection laws since at least 2012, and that senior management at the hospital was aware of the problems and did not act.

“St. Joseph placed obstacles in the way of thousands of individuals in need of affordable health care,” Ferguson said at a news conference in Tacoma announcing the lawsuit. “St. Joseph’s conduct is illegal and harms vulnerable Washingtonians.”

Washington law requires all hospitals to let patients know about the availability of charity care and to screen them for eligibility. It also limits the number of documents required of patients to prove their income. Among the allegations against St. Joseph’s is that employees were told to not volunteer information about the charity care program. When patients were able to apply for charity care, Ferguson said that St. Joseph’s required multiple income verification documents, instead of the one that is required under state law.

Ferguson also said that employees were trained to give patients the impression that they needed to pay for their treatment upfront, meaning that patients who may have been eligible for treatment ended up paying deposits of $250 or more before treatment.

CHI Franciscan Health, which runs the hospital, did not respond directly to the specific allegations raised by Ferguson. In a written statement, Cary Evans, vice president of communications and government affairs, expressed disappointment over the lawsuit.

“As a nonprofit charitable organization, we are committed to providing the highest quality care to everyone who needs it,” he wrote. “We carefully consider all charity care applications we receive and approve all who qualify.”

The hospital’s practices ultimately led to St. Joseph’s providing charity care at a lower rate than the regional average — as much as $70 million less over a four-year period, Ferguson said.

Ferguson said that not only does he wants to ensure that the hospital provides patients with notice of their rights to charity care, he is seeking restitution for the low-income patients affected, as well as civil penalties. Under the state’s consumer protection laws, civil penalties of up to $2,000 per infraction can be incurred. Ferguson noted that tens of thousands of patients were affected by the hospital’s practices.

“They’re going to be held accountable, and they will absolutely correct their practices,” Ferguson said. “They need to make changes, systemic changes, and they’re going to do it.”