Acting White House chief of staff Mick Mulvaney gave a stern warning about President Trump's upcoming decision to impose tariffs on Mexican goods in retaliation to illegal immigration.

“He is absolutely, deadly serious,” Mulvaney said on “Fox News Sunday.” “In fact, I fully expect these tariffs to go on to at least the 5 percent level on June 10th. The president is deadly serious about fixing the situation at the southern border.”

“Six months ago, we told everybody it was an emergency situation, very few people believed us,” continued Mulvaney. “It’s real. We had a group of a thousand people — not in different times — one group of a thousand people walk across the border in just the last couple of days.”

Mulvaney’s comments came after Trump announced Thursday, plans to increase tariffs “until the Illegal Immigration problem is remedied.”

“On June 10th, the United States will impose a 5% Tariff on all goods coming into our Country from Mexico, until such time as illegal migrants coming from Mexico, and into our country, STOP,” Trump wrote. “The Tariff will gradually increase until the Illegal Immigration problem is remedied at which time the Tariffs will be removed.”

Photo: Jim Watson/AFP/Getty Images

The White House later said the tariff would gradually increase to 10 percent on July 1, 15 percent on Aug. 1, 20 percent on Sept. 1, and 25 percent on Oct. 1.

Mulvaney said there are “specific things that the Mexicans can do” to reduce the flow of immigrants crossing through to the U.S.-Mexico border and thereby prevent these tariffs from increasing.

In addition to securing their southern border, which is shorter than boundary shared by Mexico and the U.S., Mulvaney said, Mexican officials “could go after their domestic terrorist organizations, their criminal organizations who are in the business of moving people across Mexico” and “make Mexico a safe place for people to claim asylum” when they come from Central American countries.

White House chief of staff Mick Mulvaney. (Photo: William B. Plowman/NBC/NBC NewsWire via Getty Images)

Trump on Sunday further threatened Mexico with tariffs, calling the country an “abuser.”

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“People have been saying for years that we should talk to Mexico,” Trump tweeted Sunday. “The problem is that Mexico is an ‘abuser’ of the United States, taking but never giving. It has been this way for decades. Either they stop the invasion of our Country by Drug Dealers, Cartels, Human Traffickers, Coyotes and Illegal Immigrants, which they can do very easily, or our many companies and jobs that have been foolishly allowed to move South of the Border, will be brought back into the United States through taxation (Tariffs).”

“America has had enough!’ he said.

Acting Department of Homeland Security Secretary Kevin McAleenan also backed Trump’s tariffs, saying “we need Mexico to step up and do more.”

“I think what the president said, what the White House has made clear is we need a vast reduction in the numbers crossing,” McAleenan said Sunday on CNN's “State of the Union.”

“These crossings into Mexico are happening on a 150-mile stretch of their southern border,” he said. “This is a controllable area. We need them to put their authorities down there and interdict these folks before they make this route all the way to the U.S.”

Mexican officials are expected to meet with Secretary of State Mike Pompeo later this week to discuss Trump’s new tariffs. But talks of a resolution, according to Trump, have been insufficient in solving “the Humanitarian and National Security Crisis” at the border.

“Mexico is sending a big delegation to talk about the Border,” Trump tweeted Sunday. “Problem is, they’ve been ‘talking’ for 25 years. We want action, not talk. They could solve the Border Crisis in one day if they so desired. Otherwise, our companies and jobs are coming back to the USA!”

Mulvaney, appearing on NBC’s “Meet the Press,” referred to Trump’s move to impose tariffs on Mexico as one of the “extraordinary tools” the U.S. is using to stop the increased flow of border crossings.

"The reason we're doing things people don't expect is that we're facing things at the border we never experienced before," he said. "We're using extraordinary tools because there are extraordinary circumstances that dictate those."

A scene from the border at Juarez, Mexico. (Photo: David Peinado/NurPhoto via Getty Images)

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