Many employers will tell employees that overtime will not be paid without the permission of a supervisor.
However, supervisors then give employees too much work to be completed in a 40-hour week, which requires the employee to work longer to avoid disappointing his/her supervisor. Then if the employee submits the time worked, it is refused because it was not approved. This is not legal.
The obligation to keep accurate records of hours worked lies with the employer, not the employee. And an employee cannot use as an excuse that approval was not given, that the employee didn’t write down the time, or something similar.