unpaid overtime
Colloquial abbreviation of サービス残業. Used in casual conversation, often with a negative connotation about working extra hours without compensation.
See also: サービス残業
I've had too much unpaid overtime this month; my body can't take it.
To reduce unpaid overtime, we need to streamline our work.
Abbreviation of サービス残業 (sābisu zangyō, 'service overtime'), where サービス implies something given for free. The exact origin is uncertain, but it likely emerged in colloquial Japanese to describe uncompensated work hours.