Later in the week, the President is expected to restrict the flow of refugees to the United States. The proposed plans include at least a four-month halt on all refugee admissions, as well as temporary ban on people coming from some Muslim majority countries, according to a representative of a public policy organization that monitors refugee issues. The person was briefed on the details of that proposed action by a government official and outlined the expected steps for The Associated Press.

The officials and the public policy organization’s representative insisted on anonymity in order to outline the plans ahead of Trump’s official announcements. The President is expected to sign the first actions Wednesday during a trip to the Department of Homeland Security, with additional actions being rolled out over the next few days, according to one official.

It appeared as though the refugee restrictions were still to be finalized. The person briefed on the proposals said they included a ban on entry to the U.S. for at least 30 days from countries including Iran, Iraq, Libya, Somalia, Sudan and Yemen, though the person cautioned the details could still change.

There is also likely to be an exception in the refugee stoppage for those fleeing religious persecution if their religion is a minority in their country. That exception could cover Christians fleeing Muslim-majority nations.

Trump campaigned on pledges to tighten U.S. immigration policies, including beefing up border security and stemming the flow of refugees. He also called for halting entry to the U.S. from Muslim countries, but later shifted the policy to a focus on what he called “extreme vetting” for those coming from countries with terrorism ties.

As president, Trump can use an executive order to halt refugee processing. President George W. Bush used that same power in the immediate aftermath of the Sept. 11 terrorist attacks. Refugee security vetting was reviewed and the process was restarted several months later.

While the specific of Trump’s orders were unclear, both administration officials said Wednesday’s actions would focus in part on the President’s plans to construct a wall along the southern border with Mexico. Trump’s insistence that Mexico would pay for the wall was among his most popular proposals on the campaign trail, sparking enthusiastic cheers at his raucous rallies.

Mexico has repeatedly said it will not pay for any border wall. Earlier this month, Trump said the building project would initially be paid for with a congressionally approved spending bill and Mexico will eventually reimburse the U.S., though he has not specified how he would guarantee payments.

Trump will meet with Mexican President Enrique Pena Nieto at the White House next week.

In claiming authority to build a wall, Trump may rely on a 2006 law that authorized several hundred miles of fencing along the 2,000-mile frontier. That bill led to the construction of about 700 miles of various kinds of fencing designed to block both vehicles and pedestrians.

The Secure Fence Act was signed by then-President George W. Bush and the majority of the fencing in Texas, New Mexico, Arizona and California was built before he left office. The last remnants were completed after President Barack Obama took office in 2009.

The Trump administration also must adhere to a decades-old border treaty with Mexico that limits where and how structures can be built along the border. The 1970 treaty requires that structures cannot disrupt the flow of the rivers, which define the U.S.-Mexican border along Texas and 24 miles in Arizona, according to The International Boundary and Water Commission, a joint U.S.-Mexican agency that administers the treaty.

Other executive actions expected Wednesday include bolstering border patrol agents and ending what Republicans have argued is a catch-and-release system at the border. Currently, some immigrants caught crossing the border illegally are given notices to report back to immigration officials at a later date.

If Trump’s actions would result in those caught being immediately jailed, the administration would have to grapple with how to pay for jail space to detain everyone and what to do with children caught crossing the border with their parents.