During the World War II the German state brought in numerous forced laborers to the city, among them many Poles. The city's economy was changed to military production-especially after the German invasion of the Soviet Union. The forced laborers were threatened with everyday harassment and repression; they were forbidden from using phones, holding cultural events and sports events, they could not visit restaurants or swimming pools, or have contact with the local German population. Poles were only allowed to attend a church mass once a month – and only in the German language. They also had smaller food rations than Germans, and had to wear a sign with the letter P on their clothes indicating their ethnic background. Additionally, medical help for Polish workers was limited by the authorities. Arrests and imprisonment for various offences, such as "slow pace of work" or leaving the workspace, were everyday occurrences.