After Constantine converted to Christianity, non-Christians in the Roman Empire were forced to ...

Not entirely sure of the answer, but here's some enlightening information:

In the fourth century AD, when Constantine became the Roman Emperor and supposedly converted to Christianity, he harnessed Political power to Religion and passed anti-Jewish laws, whereby Jews were excluded from every sphere of political influence, and denied civic rights.

The Gospel accounts began to be the source from which wrong teachings grew, until the word "Deicide" meant the Jews killed God, and were labelled "Christ-killers". Matthew 27:25 which spoke of some Jewish leaders was used instead to apply to all Jews: "His blood be on us and on our children...Ye are of your father the devil."

Converts to Christianity and converts to Judaism sparked a seriously divisive rivalry. Religious competition began between the Greek fathers of the Church, and Jews. Church laws were passed whereby Jewish relations with Christian women was now punishable by death. Anti-Semitism at this time was mainly limited to the clergy, who were the educated minority.