You can participate in a 3a restricted private pension plan if:
You already pay contributions to a 2nd pillar (generally employees).
You do not have OPA pension plan (generally self-employed persons).
You live abroad but work in Switzerland (e.g. cross-border workers).
You receive a daily allowance from Swiss unemployment insurance.
You are a partially disabled insured person with an income on which you pay OASI (AHV, AVS).
If you have reached retirement age but are still working, you can continue to pay contributions until five years after the age of 65 (men) and 64 (women).
You can continue to pay contributions even if you temporarily stop working (during civil or military service, unemployment, illness, etc.).
There are no special requirements for the 3b unrestricted pension plan.
The pension plan providers can provide you with detailed information about taking out a 3rd pillar.