A federal judge in Washington, D.C., on Wednesday blocked the Trump administration policy that restricts migrants who cross the southern border from seeking asylum.

In a 128-page order, U.S. District Judge Randolph Moss wrote that President Donald Trump cannot "adopt an alternative immigration system," saying that Trump has exceeded his legal authority as president.

In an executive order issued in January, Trump declared that the situation at the southern border constitutes "an invasion of America" and suspended the ability of migrants to seek asylum.

The Supreme Court, in a ruling last week, limited judges' power to block the president's executive orders on nationwide basis. But in his order Wednesday, Judge Moss concluded that "this is one of the rare cases in which injunctive relief is required."

Judge Moss said he recognizes that while the executive branch "faces enormous challenges in preventing and deterring unlawful entry" into the U.S., neither the Constitution nor the Immigration and Nationality Act "provides the President with the unilateral authority to limit the rights of aliens present in the United States to apply for asylum."

The federal judge granted the plaintiffs' request to certify a class of all people covered by Trump's executive order, and stayed his decision for 14 days to allow the Trump administration to appeal and to "prepare to implement the Court's order."

In response to the ruling, Lee Gelernt, an attorney with the ACLU, told ABC News that the "decision's importance cannot be overstated."

"The ruling is critical for those feeling gruesome danger and reaffirms that the president in our system of government cannot simply give the back of his hand to laws passed by Congress," Gelernt said.