The Supreme Court on Wednesday morning will hear arguments on President Donald Trump’s executive order limiting birthright citizenship. Trump will attend the hearing, making him the first president in history to sit in on a Supreme Court hearing. Beginning at 10:00 a.m. ET, the nine Supreme Court justices will hear arguments from Solicitor General John Sauer, who is defending Trump’s order, which would end the automatic grant of citizenship for anyone born on American soil, including the children of illegal immigrants. Among the groups challenging Trump’s order is the American Civil Liberties Union, whose legal director Cecillia Wang is arguing the case before the Supreme Court. The case centers on the Trump administration’s interpretation of the 14th Amendment, and the president’s attempt to clarify who qualifies as a person born in the United States and is “subject to the jurisdiction thereof.” The White House argues that the 14th Amendment “has always excluded from birthright citizenship persons who were born in the United States but not ‘subject to the jurisdiction thereof.'” Based on this understanding, Trump’s executive order states that a baby born to parents who were not American citizens or lawful permanent residents at the time of the birth should not automatically be granted citizenship. Trump’s order also states that a baby born to parents who were in the United States lawfully but only on a temporary tourist or student visa should not be granted citizenship. Trump’s birthright citizenship order was one of the many moves he made on his first day back in office last January to address illegal immigration. The president has argued that migrants often take advantage of birthright citizenship by giving birth to children on American soil after crossing the border illegally. The 14th Amendment, which was ratified just three years after the end of the Civil War, clarified that the children born to African slaves are American citizens. “Birthright Citizenship is not about rich people from China, and the rest of the World, who want their children, and hundreds of thousands more, FOR PAY, to ridiculously become citizens of the United States of America,” Trump said on Monday. “It is about the BABIES OF SLAVES!” The president’s order was never allowed to go into effect as it was blocked by federal courts around the country immediately after Trump signed it. Groups opposed to Trump’s interpretation of the 14th Amendment argue that birthright citizenship has always been understood to apply to anyone born in the United States.