"The rule is un-American, anti-immigrant and unlawful. I intend to stop it," Ferguson said as quoted by the media.
Acting US Citizenship and Immigration Services Director Ken Cuccinelli said earlier in the week that the Trump administration issued an order permitting US authorities to restrict the issuance of residence permits to immigrants who had previously enjoyed certain kinds of public benefits.
The 169-page lawsuit was filed in the US District Court in Eastern Washington, the Seattle Times said and was joined by the states of Colorado, Delaware, Illinois, Maryland, Massachusetts, Michigan, Minnesota, Nevada, New Jersey, New Mexico and Rhode Island.
The new rule is expected to enter into force in October. It will affect immigrants who have received social payments for more than 12 months in the past three years, including all forms of Medicaid health insurance and food stamp programs, and others.
According to an analysis by the Migration Policy Institute think tank, cited by the Seattle Times, approximately 150,000 non-citizens residing in the state of Washington receive at least one benefit mentioned in the new regulation.