What does it mean for foreign prisoners to be sent to immigration after they are released from prison?

Those who serve their sentences in China first shall be deported after the expiration of their sentences, and then deported by the public security organs. According to the Provisions on the Enforcement Measures for Forced Aliens to Leave the Country, foreigners sentenced to fixed-term imprisonment will be additionally punished with deportation after the expiration of the principal punishment, and the public security organs will be responsible for deportation.