The American Civil Liberties Union’s Cecelia Wang called today’s Supreme Court decision in the birthright citizenship case a “celebration,” and wished “good luck” to Republicans in Congress who attempt to change birthright citizenship law.

“Ask any American what our citizenship rule is, and they will tell you if you’re born here, you’re a citizen, just like everyone else, and that couldn’t be more fundamental to who we are as a nation,” Wang, who argued the case before the justices in April, told CNN’s Pamela Brown.

House Speaker Mike Johnson told reporters on Tuesday after the decision that Congress will deal with the idea of birthright citizenship. In his opinion, Justice Brett Kavanaugh suggested that Congress could hold statutory power under the Constitution to limit birthright citizenship, despite his ultimate decision to rule with the majority that the president’s executive order was illegal.

“If they want to try and overturn it by constitutional amendment, good luck to them, because they’re going against the will of the people of this country of the United States,” Wang said.

In April, Wang argued that President Donald Trump’s Executive Order should not hold, and she told the justices that if Congress did not want the Fourteenth Amendment to cover immigrants, that the law would have said so.

“So the Fourteenth Amendment’s birthright citizenship clause, as part of the Reconstruction Amendments of the Constitution, were hard won by African Americans who fought for freedom, who fought to end the notion of caste in this country,” Wang said Tuesday.

“So President Trump, in this executive order, and in so many of his other executive actions, was trying to talk about immigration, but what he was doing was profoundly well beyond immigration policy.”