The Trump administration is set to harden the rules this week on those allowed to seek asylum in the United States, as it attempts to stem a wave of migration on its southern border with Mexico.

In a fast-track regulation set to publish in the Federal Register on Tuesday, the administration has created a framework that will allow asylum seekers to be sent to other nations that have negotiated bilateral agreements to accept them.

Previously, officials in the administration of US President Donald Trump have argued that migrants with a valid need for asylum should seek protection in the first ‘safe’ country where they have the chance to apply, since many migrants travel through multiple countries on their way to the US border.

However, the new regulation states that asylum seekers may be sent to any other countries with which the United States has asylum agreements that permit such an action - even if they did not first transit through those nations.

The regulation is the latest action by Trump to restrict asylum access in the United States. Trump has made immigration - and curbing the number of mostly Central American migrants arriving at the border - a major theme in his reelection campaign.

The United States already maintains a bilateral asylum deal with Canada. Guatemala, El Salvador and Honduras have also signed such deals in recent months, but the pacts have not been finalized.

The regulation released on Monday will amend US guidelines to permit similar deals with other nations.

Other Trump measures have sought to restrict asylum eligibility or force migrants to wait in Mexico pending the resolution of their claims, but not force asylum seekers to pursue their claims in another country.

Migrants who may be sent to a third country under the new regulation will have an opportunity to prove that they’re “more likely than not” to be persecuted or tortured in that country, but advocates argue that will be a high hurdle.

Aaron Reichlin-Melnick, policy counsel at the pro-migrant American Immigration Council, said the regulation could reshape the US asylum system.