Early in their history the Romans adopted the system of contracting out the task of tax collection. The person who was awarded the contract agreed to pay a certain amount into the treasury ("in publicum"). The group thus received the name of "publicani." They were able to extort much more from the people than they had contracted to pay to the treasury, and thus they earned the general reputation of being greedy and venal.
As a matter of course, the tax collectors overcharged wherever they could (Luke 3.13). They often brought false smuggling charges against someone to secure bribes that would then cover up the accusation (Luke 19.8). Although the chief tax collectors were Roman, they hired local people to administer the program throughout the empire. All the tax collectors mentioned in the Gospels are Jewish.
Jewish tax collectors were doubly despised by the religious leaders. First, their trade was dishonest and parasitic; the tax collectors profited from cheating their own people. And second, the tax collectors were in daily, intimate contact with the Gentile occupation government. This rendered the tax collectors ceremonially unclean. Such uncleanness was not of the inadvertent kind but was deliberate and systematic. Tax collectors were, therefore, considered to be religiously defiled traitors who furthered the fortunes of the oppressor out of the pockets of God's people.
The experts taught that anyone who ate with a tax collector defiled himself They lumped tax collectors and sinners together as people who were wholly unacceptable as associates. Some of John the Baptist's disciples were tax collectors, as were some of Jesus' earliest followers. Matthew collected the taxes for the city of Capernaum. Jesus often dined with tax colletors and their friends, to the dismay of the religious leaders. Zacchaeus, a subcontractor for the taxes of Jericho, had many tax collectors working for him.