3,631. Non-Jews and Challah

Hilchos Bikkurim 6:9

If a non-Jew and a Jew jointly owned a dough and the portion owned by the Jew was large enough to require that challah be taken, then challah must be taken.

Hilchos Bikkurim 6:10

If a non-Jew takes challah even in Israel, what he separates is not rendered challah. Rather, he is informed that he is not obligated in this mitzvah. The dough that he took may be eaten by a non-kohein. We are not concerned that the dough might belong to a Jew, who gave it to the non-Jew in order to exempt it from challah. This is because if a Jew wanted to exempt himself from challah, all he would have to do is make a smaller dough.