In the West, you need special permission to become a priest if you are married because the Latin Church has ruled that it will only ordain celibate men. This special permission is typically only given to clerical converts from other closely-Catholic Christian sects (i.e. your average Baptist pastor would likely not be granted this permission).
In the East, you do not need special permission. While celibacy is seen as the preferred state for a priest, there is no rule against the ordination of married Catholic men.