Democratic attorneys general on Tuesday filed lawsuits in Massachusetts and Washington state seeking to block President Donald Trump‘s attempt to revoke the right to automatic birthright citizenship. Trump on Monday signed an executive order that purports to limit birthright citizenship to people who have at least one parent who is a United States citizen or a permanent resident. The proposal faces an uphill battle and strong opposition not just from 23 Democratic attorneys general, including officials from New Jersey, California, New York, Massachusetts and the District of Columbia, but also civil rights groups, who have already filed their own lawsuit. “This is a war on American families waged by a president with zero respect for our Constitution. We have sued, and I have every confidence we will win,” said Connecticut Attorney General William Tong. He and 18 other attorneys general filed their lawsuit in Massachusetts federal court. Four states, Washington, Arizona, Oregon and Illinois, filed the other lawsuit. The Massachusetts lawsuit calls Trump’s plan a “flagrantly unlawful attempt to strip hundreds of thousands [of] American-born children of their citizenship based on their parentage.” Trump’s proposal seeks to “abrogate this well-established and longstanding constitutional principle by executive fiat,” the lawsuit says. The lawsuit filed in Washington says that the states would “suffer immediate and irreparable harm” if the measure is implemented, with thousands of people affected. Nationwide, about 12,000 babies born each month “will no longer be considered United States citizens,” the lawsuit says. It has long been accepted that the Constitution’s 14th Amendment guarantees the right to birthright citizenship for anyone born in the United States, with the exception of the children of diplomats. “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States,” the amendment says. Trump’s proposal does not go into effect for a month, giving courts ample time to block it before then. The federal district court in Massachusetts is within the jurisdiction of an appeals court dominated by Democratic-appointed judges. The Supreme Court ruled in 1898, in a case called United States v. Wong Kim Ark, that a man born in San Francisco to parents who were both from China was a U.S. citizen. Many legal experts believe that the court, despite having a 6-3 conservative majority including three Trump-appointed justices, would likely reject the administration’s novel interpretation of the law. This story first appeared on NBCNews.com. More from NBC News: Trump’s contentious executive orders expected to face legal challenges Trump issues a slew of immigration-related executive orders on first day of new term Investment firm CEO offers to take Vivek Ramaswamy’s spot at DOGE