My understanding was that they could not legally force you into enrolling in the National Pension ( 国民年金; kokumin nenkin). They could coerce, cajole or fool you into enrolling - but if you knew what you were doing, you could legally avoid enrolling into it.
However, a friend claims that with some of the recent changes such as the old Social Insurance Agency (SIA) being rolled into the new Japan Pension Agency, the legal obligation to enroll has been strengthened similar to that of the legal obligation to pay one's taxes. He did not provide any laws or information for reference.
Of course, I can see plenty of references which indicate that "all registered residents of Japan, both Japanese and foreign, are required to enroll in the national pension system" - however, my understanding is that it holds the same amount of (legal) water as the Broadcast Law that states "Any person who has installed receiving equipment capable of receiving the broadcasting provided by NHK shall conclude a contract with NHK with regard to the reception of its broadcasting. " In other words, unenforceable.
Any legal eagles out there who might be able to clarify my concerns?
The way I see it, I have no financial incentive to enroll in such a program. Better to put the equivalent amount of dues into my own investments.