MEXICO CITY (AP) — U.S. Ambassador to Mexico Ken Salazar warned Thursday that migrants who do not opt for a legal pathway into the U.S. will face great consequences, a message coming at a time when the Biden administration needs Mexico’s cooperation in easing the flow of migrants to their shared border.

Salazar told reporters that the number of migrants arriving at the U.S.-Mexico border has dropped since U.S. President Joe Biden implemented changes last week aimed at making it more difficult for those seeking asylum. But he did not specify by how much the number of migrant encounters had dropped.

“If they don’t arrive in a legal manner, there will be consequences,” he said. “They will be returned to their home countries and will not be allowed into the United States for five years.”

Biden’s executive order would limit asylum processing once encounters with migrants between ports of entry reach 2,500 per day. It went into effect immediately because the latest figures were far higher, at about 4,000 daily.

Civil rights groups have been quick to react to the policy changes. A coalition of immigrant advocacy groups on Wednesday sued the Biden administration saying the presidential order differs little from a similar move by the Trump administration that was blocked by the courts.

South of the border, Mexican authorities have been rounding up migrants, including those returned by the U.S., and taking them to the southern cities of Villahermosa and Tapachula in an effort to discourage them from migrating north.

The head of the U.N. refugee agency cautioned Thursday that some aspects of Biden’s order may violate refugee protections required by international law.

Immigration cooperation was also among the topics discussed Thursday when U.S. Vice President Kamala Harris called incoming Mexican President Claudia Sheinbaum to congratulate her on her victory, according to a statement from Harris’ office.

“Our objective is clear,” said Salazar. “We want to deepen the relationship between the U.S. and Mexico as neighbors, economic partners, and as a family.”

Salazar declined to offer his opinion on controversial judicial reforms proposed by outgoing Mexican President Andrés Manuel López Obrador.

Earlier this week, Brian Nichols, U.S. assistant secretary for Western Hemisphere affairs, urged that there be transparency in Mexico’s judicial reforms, particularly concerning any impact they could have on U.S. investors and companies.

Salazar said that a strong judicial system was important, but it was up to Mexicans to decide on the changes.