WASHINGTON, June 3 (Xinhua) -- U.S. scholars and business groups have questioned the legality of President Donald Trump's authority to impose tariffs on imports of Mexican goods due to immigration concerns.

Trump said on Thursday that he would impose a 5-percent tariff on all imported Mexican goods beginning June 10 so as to pressure the country to halt undocumented migrants crossing the border, and will gradually increase tariffs until the problem is remedied.

The unprecedented move, citing the president's authority under the International Emergency Economic Powers Act (IEEPA) of 1977, immediately drew wide-ranging criticism from politicians, scholars and business leaders across the country.

"Trade policy and border security are separate issues," Republican senator Chuck Grassley, chairman of the Senate Finance Committee, said Thursday in a statement. "This is a misuse of presidential tariff authority and counter to congressional intent."

Jennifer Hillman, a professor of practice at the Georgetown Law Center, believed that the U.S. president could impose tariffs only in cases where Congress has "clearly delegated" the power to do so.

"I don't read IEEPA as a clear delegation of power to impose tariffs. Probably why no President has ever used IEEPA to impose tariffs," Hillman wrote on Twitter.

Edward Alden, a senior fellow at the Council on Foreign Relations, said the purpose of IEEPA was to give the president tools to impose economic sanctions on America's enemies and adversaries in the face of "unusual and extraordinary threats."

"It was never intended to give the president carte blanche authority to impose tariffs on close allies," Alden wrote in a blog post on Friday, noting that using IEEPA to justify tariffs is "a flagrant abuse of the congressional statute."

"If the Congress lets Trump get away with this, he will be free to slap tariffs on any country or any product at any time for whatever reason he dreams up," he argued, adding that the president's decision to link trade to immigration and refugee concerns is an "especially dangerous escalation."

Markets will realize that it's not likely for the U.S. president to deliver a trade deal with its trade partners if tariffs can be raised by "unilateral presidential decree," linked to border policy not the economic relationship, said Adam Posen, president of the Peterson Institute for International Economics.

Analysts and lawmakers have also argued that the proposed tariffs on Mexican goods could violate the rules of the North American Free Trade Agreement (NAFTA) and World Trade Organization (WTO).

"This decision also threatens to upend 25 years of duty-free treatment for products that cross the U.S.-Mexico border, and violates longstanding American commitments under NAFTA and at the World Trade Organization," Republican Senator Pat Toomey of the state of Pennsylvania said in a statement.

"The president's use of tax hikes on Americans as a tool to affect change in Mexican policy is misguided. It is past time for Congress to step up and reassert its Constitutional responsibility on tariffs," Toomey said.

"If the Republican Senate Majority does not show backbone in standing up to President Trump on this abuse, and if it lets stand the administration's usurpation of Congressional prerogatives in the trade and foreign policy areas, that alone will reinforce the markets' correct perception that the world has become too uncertain for many investments," Posen noted.

Neil Bradley, executive vice president and chief policy officer at the U.S. Chamber of Commerce, said the chamber was exploring legal options to challenge U.S. tariffs on Mexican goods.

"We have no choice but to pursue every option available to push back," Bradley said, adding that these tariffs will be paid by American families and businesses without doing a thing to solve the very real problems at the border.

Tariffs Hurt the Heartland, a national campaign comprised of over 150 of America's largest trade organizations from across retail, tech, manufacturing and agriculture, also blasted the president's tariff decision.

"Using tariffs to address unrelated policy objectives sets a dangerous precedent while creating significant uncertainty for American employers who are living tweet-by-tweet while trying to plan their business," the groups said in a statement.