US President Donald Trump tweeted on Tuesday night, "Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!"
During his election campaign, Trump met with Mexico's President Enrique Pena Nieto to discuss the construction of a wall separating the two countries. Nieto said his government will negotiate with Trump, but will not pay for the wall - despite Trump's insistence he do so.
According to the New York Times, Trump is expected to sign on Wednesday night the executive order during an appearance at the Department of Homeland Security.
A senior Trump administration official told NBC News Trump expects Mexico to pay for the wall, eventually. The official also said Trump is expected to tackle more immigration-related issues this week.
Reports also claim Trump is considering a policy to temporarily prevent refugees from "terror-prone" Muslim countries from entering the US.