GOP lawmakers responded warily to President Trump's announcement of new tariffs on steel and aluminum Thursday, with House Speaker Paul Ryan, R-Wis., asking the president to "consider the unintended consequences of this idea."

In a statement, Ryan suggested that Trump "look at other approaches before moving forward."

Trump has been facing a pair of April deadlines to make a decision on the imports. Key Senate offices did not receive notice about Thursday's announcement, and the Associated Press reported that even some top White House officials were caught off guard.

Sen. Ben Sasse, R-Neb., one of Trump's most prominent Republican critics, slammed the tariffs as "a massive tax increase on American families."

"Protectionism is weak, not strong," Sasse said. "You'd expect a policy this bad from a leftist administration, not a supposedly Republican one."

Other lawmakers raised concerns the tariff announcement would launch a trade war that could hurt other industries.

"Every time you do this, you get a retaliation and agriculture is the No. 1 target," said Sen. Pat Roberts, R-Kan., chairman of the Senate Agriculture Committee. "I think this is terribly counterproductive for the ag economy."

"I just don't think that's the way to go," said Sen. Orrin Hatch, R-Utah, who added in a statement that the American people "don't need and can't afford" the tariffs.

Trump, in announcing he would pursue tariffs of 25 percent for steel and 10 percent for aluminum earlier in the day, said it would level the playing field for American companies and help them expand after plant closings in recent years.

“So steel and aluminum will see a lot of good things happen,” Trump told reporters at the White House. “We're going to have new jobs popping up."

"You will have protection for the first time in a long while and you are going to regrow your industries," Trump also told industry executives. "That's all I'm asking. You have to regrow your industries."

But Pennsylvania Sen. Pat Toomey argued that current U.S. policy to counter illegal steel trading has been "reasonable" and "successful."

"The vast majority of the steel Americans consume is domestically produced, which is the way I prefer it," Toomey said in a statement. "[I]nvoking national security as a means of imposing new, huge tariffs on all kinds of imported steel is a big mistake that will increase costs on American consumers, cost our country jobs, and invite retaliation from other countries.”

Trump last year ordered an investigation into whether aluminum and steel imports posed a threat to national defense. Commerce Secretary Wilbur Ross said last month that the imports "threaten to impair our national security," noting, for example, that only one U.S. company now produces a high-quality aluminum alloy needed for military aircraft.

Section 232 of the Trade Expansion Act of 1962 gives the president authority to restrict imports and impose unlimited tariffs if a Commerce Department investigation finds a national security threat.

The Associated Press contributed to this report.