annual income threshold (affecting taxes or social insurance)
Refers to a specific income level where tax or social insurance burdens increase, often discussed in the context of part-time workers adjusting hours to stay below the threshold.
Housewives working part-time adjust their working hours so as not to exceed the annual income threshold.
If the annual income threshold is raised, more people will be able to work more.
Compound of 年収 (annual income) + の (possessive particle) + 壁 (wall), literally 'wall of annual income'. The term metaphorically describes an income barrier that triggers higher tax or social insurance payments.