Read Leviticus 25:53 Using Other Translations
And as a yearly hired servant shall he be with him: and the other shall not rule with rigour over him in thy sight.
He shall treat him as a servant hired year by year. He shall not rule ruthlessly over him in your sight.
The foreigner must treat them as workers hired on a yearly basis. You must not allow a foreigner to treat any of your fellow Israelites harshly.