The Trump administration has turned to tariffs on imports of all Mexican goods as a prod to the Mexican government to step up its efforts to stem the flow of Central American migrants to the U.S. southern border.

Acting White House Chief of Staff Mick Mulvaney and acting Homeland Security Secretary Kevin McAleenan told reporters in a conference call Thursday night that the thousands of people crossing the border had reached a crisis point and now constitute a national security threat. They said an average of 4,500 people per day for the past 21 days have come across the border from Mexico.

A 5 percent tariff on Mexican goods would take effect June 10 and rise in stages to 25 percent on Oct. 1 if Mexico doesn’t take action to slow illegal migration to the U.S.

While the Trump statement announcing the tariffs largely blamed Mexico for problems at the border, Mulvaney also blamed Congress for not providing the administration additional border funding it requested. Border funding has become a flashpoint between the administration and congressional Democrats.

“This is an urgent problem,” Mulvaney said. “We’re interested in seeing the Mexican government react tonight, tomorrow.”

McAleenan said the border situation is a “national emergency” and that border crossings in May are on track to surpass the record of 109,000 crossings in April. McAleenan and Mulvaney said Congress had failed to act for four weeks on a supplemental funding request.

Mulvaney said the administration had briefed some Republican senators about the proposed tariffs on Mexico but had not spoken with Democrats.

Senate Finance Chairman Charles E. Grassley sharply disagreed with the administration’s use of tariffs.

“This is a misuse of presidential tariff authority and counter to congressional intent,” the Iowa Republican said in a statement.

Mulvaney said the tariffs should not affect the administration’s effort to get the proposed United States-Mexico-Canada Agreement, or USMCA, ratified in Mexico. The new trade deal would replace the 1994 North American Free Trade Agreement if the national legislatures in all three countries approve the proposed trade pact.

“These are not tariffs as part of a trade dispute. These are tariffs that are part of an immigration matter,” Mulvaney said.

But Grassley, whose committee would oversee the handling of the proposed NAFTA replacement, said imposing the tariffs could undermine passage of the trade agreement.

“Following through on this threat would seriously jeopardize passage of USMCA, a central campaign pledge of President Trump’s and what could be a big victory for the country,” he said. “President Trump should consider alternatives, such as imposing a fee on the billions of dollars of remittances that annually leave the United States to Mexico, which only encourage illegal immigration and don’t help the U.S. economy.”

Earlier this month, the Trump administration ended Section 232 steel tariffs of 25 percent and aluminum tariffs of 10 percent on products from Mexico and Canada. Both countries had threatened to delay ratification of the new trade agreement until the duties were lifted. Each country submitted implementing legislation for the agreement this week.

Demands on Mexico

When asked if the tariffs could constitute a tax that Americans will pay rather than Mexico, Mulvaney said taxpayers are footing the bill now for increased enforcement at the border because of the many migrants.

He said there was no specific numeric reduction Mexico had to achieve.

McAleenan said Mexico could crack down on illegal immigration by stopping more people at its border with Guatemala, targeting the transnational criminal networks of smugglers who move people across the border, and requiring asylum seekers to make their applications in Mexico rather than going on to the U.S.

In a statement Thursday, President Donald Trump accused Mexico of “passive cooperation” in allowing migrants to cross its territory for the U.S.

He said he would impose tariffs under authorities granted by the International Emergency Economic Powers Act.

“If the illegal migration crisis is alleviated through effective actions taken by Mexico, to be determined in our sole discretion and judgment, the tariffs will be removed,” Trump said, adding that if they rise to the top level, “tariffs will permanently remain at the 25 percent level unless and until Mexico substantially stops the illegal inflow of aliens coming through its territory.”

Trump said Mexico should use its “very strong immigration laws and could easily halt the illegal flow of migrants, including by returning them to their home countries. Additionally, Mexico could quickly and easily stop illegal aliens from coming through its southern border with Guatemala.”

Although Mulvaney said the tariffs had nothing to do with trade, the president also said he saw gains for the U.S. economy if high tariffs could cause companies to move from Mexico to the U.S.

“Companies that relocate to the United States will not pay the Tariffs or be affected in any way,” Trump said. “Should Mexico choose not to cooperate on reducing unlawful migration, the sustained imposition of Tariffs will produce a massive return of jobs back to American cities and towns.