A lot of reasonable people define forced labor as slavery:

The condition of a slave; the state of entire subjection of one person to the will of another.

A condition of subjection or submission characterized by lack of freedom of action or of will.

Forced labour, or unfree labour, is sometimes used to describe an individual who is forced to work against their own will, under threat of violence or other punishment. This may also include institutions not commonly classified as slavery, such as serfdom, conscription and penal labour. As slavery has been legally outlawed in all countries, forced labour in the present day (frequently referred to as "modern slavery") revolves around illegal control.