U.S. President Donald Trump is expected to sign executive orders starting on Wednesday that include a temporary ban on most refugees and a suspension of visas for citizens of Syria and six other Middle Eastern and African countries, say congressional aides and immigration experts briefed on the matter.

Trump, who tweeted that a “big day” was planned on national security on Wednesday, is expected to ban for several months the entry of refugees into the United States, except for religious minorities escaping persecution, until more aggressive vetting is in place.

Another order will block visas being issued to anyone from Syria, Iraq, Iran, Libya, Somalia, Sudan and Yemen, said the aides and experts, who asked not to be identified.

In his tweet late on Tuesday, Trump said: “Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!”