Romans were tolerant of other religions unless what?

Unless it supported another regime or political leaning than the support of the Caesar. For instance the Jews, when looking to execute Jesus, claimed that they were doing so to support Caesar as king instead of Jesus. (John 19:14-15) The early Christians also were persecuted because they viewed Jehovah God's kingdom as superior to the Roman government, and the religious leaders of the day egged on Roman authorities to do so. One of the most popular examples is the case with Pontius Pilate and the trial of Christ. (Luke 23:13-25)

(New World Translation of the Holy Scriptures)