WASHINGTON, March 18 (Xinhua) -- A coalition of free-market advocacy and business groups on Monday urged the Senate Finance Committee leaders to push for new legislation to rein in the tariff authority of the White House.

In a letter addressed to committee chairman Chuck Grassley and ranking member Ron Wyden, the coalition of 30 groups, including the Americans for Prosperity and Freedom Partners Chamber of Commerce, asked lawmakers to consider legislation that would require Congress to approve any tariff increases proposed by the president before the tax is allowed to take effect.

"The scope of legislation should apply to all instances where the president has been delegated authority to impose tariffs, including Section 232, Section 301, and others," the letter continues.

"The term 'national security' should be specifically defined in law to guide investigations for proposing tariffs under Section 232, and proposed barriers to trade under this authority should only be implemented for narrowly tailored, well-defined national security interests," the coalition said.

A number of lawmakers have introduced bills to curb the president's authority to use Section 232 of U.S. trade law to impose tariffs, and the Senate Finance Committee has a big say in deciding which bill could be brought up for a vote.

In February, Republican Senator Rob Portman and a few other senators introduced a bipartisan bill called the "Trade Security Act," which would require the U.S. Defense Department to justify the national security basis for new tariffs under Section 232 and "increase congressional oversight" of this process.

The Trump administration has repeatedly invoked the previously seldom-used Section 232 of the Trade Expansion Act of 1962, allowing it to impose tariffs on imported products on national security grounds.

"The president has unilaterally imposed tariffs -- which are taxes on Americans -- on more than 300 billion U.S. dollars in imports last year without the explicit approval of the people's elected representatives in Congress," the letter read.

Last year, the administration unilaterally slapped tariffs on imported steel and aluminum products citing Section 232 investigation, provoking retaliation from trading partners including Canada, Mexico and the European Union.

In February, the U.S. Commerce Department has concluded a Section 232 report on imported cars and parts, and in July last year, it has launched investigations into uranium imports, and most recently, it initiated its probe into titanium sponge imports earlier this month.