The charity has welcomed a report by the UN Special Rapporteur on the Situation of Human Rights in North Korea.
It noted that "a number of long-standing and ongoing patterns of systematic and widespread violations in [North Korea] met the high threshold required for crimes against humanity in international law".
The study also found the crimes "clearly merit a criminal investigation".
North Korea has repeatedly been criticised for cracking down on Christianity and other religions.
Earlier this year an American man was arrested for having a Bible - although he's now been released.
CSW's East Asia Team Leader Benedict Rogers said: "We warmly welcome the Special Rapporteur's report, and the proposed draft resolution on North Korea currently before the General Assembly.
"We urge the General Assembly to adopt the Special Rapporteur's recommendations. The case for action is now overwhelmingly clear and long overdue.
"The need is urgent. It is time to end impunity, hold those responsible for crimes against humanity to account, and to exercise international responsibility to protect the people of North Korea".