It's in response to the administration's directives that would withhold funds from hospitals that treat transgender youth.
University of Illinois Hospital on Friday became the fourth in Chicago to pause gender affirming care for young people.
Attorney General Kwame Raoul and his counterparts from more than a dozen other states are now suing to block the president's executive orders.
SEE ALSO | UChicago Medicine pausing gender-affirming care for child patients
It's a battle that started as soon as President Donald Trump took office, when he signed a series of executive orders, directing agencies to take steps to ensure that hospitals receiving federal research and education grants do not offer care for transgender youth.
The threat of subpoenas and possible prosecutions have followed in other states. The University of Illinois Hospital announced that it has now paused transgender surgeries for anyone under 19 effective Friday, after reviewing federal actions.
"Since taking office, President Trump and his administration have relentlessly, cruelly and unlawfully targeted transgender individuals," Raoul said.
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Lurie Children's Hospital was the first to stop offering transgender surgeries to youth back in January.
University of Chicago Medicine followed suit last month.
Rush Hospital also paused care, which advocates say is necessary for young people experiencing gender dysphoria.
SEE ALSO | Chicago Lurie Children's Hospital responds to Trump executive order on transgender care
"The administration has overstepped its authority by using threats of federal investigation and criminal prosecution under laws that do not apply in this case. These threats have pressured providers to stop offering life-saving care," Raoul said.
"My hope that this lawsuit will again send a resounding message to our federal administration that we are not just going to lay down," said Channyn Lynne Parker, the CEO of the Brave Space Alliance.
Opponents of gender-affirming care support the president's actions.
"And so by restricting funding to hospitals, this is the mandate, protect children, give them compassionate care, ethical care, follow the Hippocratic Oath, but stop this abuse of children, stop the mutilation and sterilization of these kids," said Shannon Adcock, president of Awake Illinois.
The lawsuit is asking a federal judge to block enforcement of the president's orders, which would allow hospitals to resume transgender care for youth.