Mick Mulvaney, acting White House chief of staff, said on "Fox News Sunday" that the tariffs were "not interrelated" with the U.S. -Mexico-Canada trade deal, known as the USMCA, awaiting approval by the U.S. Congress.
On Friday, Mexico's top farm lobby said Lopez Obrador should target agricultural goods from states that support Trump's Republican Party if the U.S. leader carries out his threat to punish Mexico for the migrants heading north.
Mexico's Economy Minister Graciela Marquez said on Sunday she would meet with U.S. Commerce Secretary Wilbur Ross in Washington on Monday, two days before the neighboring countries are due to discuss possible tariffs on Mexican goods.
Trump declared a national emergency at the U.S. -Mexico border in February, in the midst of a government shutdown over Congress' refusal to grant significant funds for a border wall, which he deems necessary to tackle the "crisis" of thousands of undocumented migrants crossing the United States southern frontier. "I don't think the president's going to impose these tariffs".
Trump appeared to have no regrets about the move, tweeting on Saturday: "When you are the "Piggy Bank" Nation that foreign countries have been robbing and deceiving for years, the word TARIFF is a lovely word indeed!"
Following an agreement with Lopez Obrador, U.S. authorities have since January begun sending migrants back to Mexico to wait there while their U.S. asylum claims are being processed.
Trump said the import tax will increase by 5 percent every month through October, topping out at 25 percent.
The impact of new tariffs would be devastating for Mexico, which sends 80 percent of its exports to the US. "Could be fixed so easily if they would vote with Republicans to fix the loopholes!" he tweeted.
China to Create Blacklist of 'Unreliable' Foreign Firms, Individuals
As a result, Huawei is losing access to key components and software needed to produce its Android smartphones and Windows laptops. The US-China trade war is heating up, and now China is creating a blacklist of US firms, and even individuals.
That new deal is the cornerstone of Trump's legislative agenda and seen as beneficial to his re-election effort. John Neely Kennedy (R-La.) called Trump's move a "mistake".
Trump had harsh words for Mexico again on Sunday morning, questioning the value of talks, days before a high-level delegation from Mexico is expected to meet with United States officials.
Ebrard is expected to meet US Secretary of State Mike Pompeo on Wednesday."We will be firm and we will defend the dignity of Mexico", Ebrard said.
Asked about what specifically Mexico would have to do to stem the flow, Mulvaney said there were "several" things, including securing their southern border with Guatemala.
The administration wants Mexico to crack down on illicit businesses that profit from transporting migrants through the country on their trip north, allow more migrants to seek asylum in Mexico instead of the United States and stop migrants from entering Mexico from Central America in the first place.
"There are specific things that the Mexicans can do", he said.
Mulvaney insisted that Trump's threat is real.
Mulvaney also blamed Democrats in Congress for not supporting Trump's border agenda, which Mulvaney said caused the president to seek ways to apply direct pressure on Mexico.
Meanwhile, some Mexican business groups have urged the government to strike back against any Trump tariffs.