open shop system
A labor policy where a workplace may hire both union and non-union workers, without requiring union membership as a condition of employment. Contrasts with ユニオンショップ制 (union shop).
Antonyms: ユニオンショップ制
Because this company uses an open shop system, you can work there even if you are not a union member.
union shop system
From English 'open shop' plus 制 (system).