President Obama's decision to relaxes rules for younger illegal immigrants was proceeded by a letter two weeks ago from nearly 100 law professors backing his plan to use prosecutorial discretion.

"Dear Mr. President," the letter stated, "there is clear executive authority for several forms of administrative relief." They outlined the route President Obama announced today called "deferred action" for potential DREAM Act beneficiaries.

They said it "can prevent an individual from being placed in removal proceedings, suspend any proceedings that have commenced, or stay the enforcement of any existing removal order."

"Though no statutes or regulations delineate deferred action in specific terms, the U.S. Supreme Court has made clear that decision to initiate or terminate enforcement proceedings fall squarely with the authority of the Executive."

The principal drafter of the letter was Hiroshi Motomura, a Professor of Law at UCLA School of law.

But critics of today's action say that Secretary Napolitano does not have the authority to issue the "deferred action" based on "prosecutorial discretion" because in 1996 Congress took away prosecutorial discretion in cases of aliens who are unlawfully in the country and when an immigration official has become aware of the situation.

"Today President Obama is claiming that he has prosecutorial discretion to refuse to deport these aliens, he is either unaware or ignoring the fact that Congress expressly removed that prosecutorial discretion in 1996, and therefore President Obama is breaking federal law," says Kris Kobach, a harsh critic of the President's immigration policy who is currently serving as Kansas Secretary of State.

"The president's actions are deeply problematic on three levels. 1) he's breaking federal law by doing this 2) he is violating his constitutional obligation to enforce the law against illegal aliens and 3) he is violating the separation of powers by seizing authority from congress."

But supporters of the president's action say the notion that Napolitano has no prosecutorial discretion is incorrect.

"The 1996 law focused on restricting the ability of federal courts to overturn immigration agency decisions -it did not address the rule of the executive branch on this particular issue. Deferred action is a long standing form of administrative relief used by presidents of both parties over many years. The action today simply extended prosecutorial discretion policy that had already been in place," says Stephen Yale-Loehr, a professor of immigration law at Cornell law school.

Contacted today, Motomura says the critics are not distinguishing between discretion to identify people for possible deportation "and discretion to carry through with actual proceedings."

"One can question the wisdom of today's move, and can debate how much the president can step into vacuums, but I don't think it's plausible to argue there is no prosecutorial discretion at all, says Motomura.

Republican Congressman Steve King of Iowa issued a statement lambasting the president's decision pointing out that the Dream Act had been rejected by Congress.

"The American people have rejected amnesty because it will erode the Rule of Law. In much the same way, I believe the American people will reject President Obama for his repeated efforts to violate the Constitutional separation of powers."