A dirty little secret of one Japanese "office lady" stereotype is that some women, dissatisfied with their clerical salaries, augment their earnings by moonlighting as bar hostesses.

The second job is not necessarily one they want revealed — carrying, as it does, images of ladies of the night in flashy dresses and makeup, entertaining salarymen with lascivious lights in their eyes.

But the upcoming introduction of the 12-digit My Number identification code assigned to all residents in Japan threatens to expose their nocturnal identity. Tax professionals say it may force some to consider abandoning their second job, often the more lucrative.