The Justice Ministry website was offline overnight through Tuesday in an apparent cyberattack, with hacker group Anonymous criticizing the ministry over its immigration policy on Twitter.

Users were unable to access the websites of the Justice Ministry and the Immigration Services Agency for about 50 minutes from 11 p.m. on Monday. After the websites were brought back online, they went offline again from 2:30 a.m. Tuesday, according to the Justice Ministry.

“Relevant departments are looking into what caused (the website to go offline),” Justice Minister Ken Saito told reporters Tuesday morning.

The website loaded Tuesday morning but was still inaccessible at times during the afternoon.

The ministry is aware of the Anonymous post criticizing Japan’s immigration policy, which also included screenshots appearing to show the ministry website as unavailable in a browser and when checked with a website testing tool, but it has not yet determined whether they caused the site's failure.

“We oppose this inhuman practice and warn the Japanese government,” Anonymous posted on Twitter early Tuesday morning. “Protect the refugees! Do not return!”

A government-sponsored immigration bill, which will allow immigration authorities to deport asylum seekers if they have applied for refugee status three times or more, is currently being deliberated in parliament.