President Donald Trump is expected to start issuing his long-anticipated executive orders on illegal immigration today with funding for his controversial Mexican border wall, and refugee restrictions aimed at stopping terrorists to follow later in the week, administration officials told reporters.

On his personal Twitter account last night, Trump tweeted: “Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!”

The president is expected to sign the first actions today during a trip to the Department of Homeland Security, with additional actions being rolled out over the next few days, news agencies reported.

Trump will issue an order to divert federal funds to start his promised border wall, the New York Times reported. 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 enforce that. Trump will meet with Mexican President Enrique Pena Nieto at the White House next week.

Other executive actions likely today include bolstering the ranks of border patrol agents and ending what Republicans have criticized as a catch-and-release system, with detained illegals freed with notices to report back to immigration officials at a later date.

He is also expected to take controversial steps to slow the flow of refugees into the country later this week, with a four-month halt on all refugee admissions and a temporary ban on people coming from some Muslim majority countries, the Associated Press reported, citing an official from a public policy organization that monitors refugee issues who was briefed on the proposed actions by a government official.

Trump drew fire with his campaign trail remarks that he would build a wall and ban Muslim immigration — the latter later amended as a temporary halt with increased vetting of people from Muslim nations that are hotbeds of terrorism.

The refugee restrictions are reportedly still being finalized. The person briefed on the proposals told the AP they included a ban on entry to the U.S. for at least 30 days from Syria, Iran, Iraq, Libya, Somalia, Sudan and Yemen.

There may be an exception for religious minorities, such as Christians who have been violently persecuted in some Muslim-majority nations.

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. President Obama made extensive use of executive orders to effect policy when he was unable to pass measures through Congress. The Republican Congress is more amenable to Trump’s proposals and already has begun working with him on some immigration measures, however, executive orders will allow swift action on his campaign priorities.