A judicial order stayed the deportation of people from seven Muslim-majority countries who arrived in the U.S. after President Donald Trump barred their entry through an executive order. 

Rationale behind judicial order
The judicial order argued that the order to ban entry of muslims could be deemed unconstitutional as it effectively sanctions religious discrimination.
Status of Judiciary in USA

Judiciary in America enjoys larger powers than Executive and Legislature in USA.  

Background
U.S. President Donald Trump had banned people from seven Muslim-majority countries from entering the nation for 90 days and suspended admission of refugees for 120 days through an executive order. The order had also indefinitely barred refugees from Syria.