The Shulhan Aruch (Orah Haim 306:5) rules that it is forbidden for a congregation to hire a Hazan to lead the services on Shabbat. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) explains that the Sages enacted a prohibition against "Sechar Shabbat" – accepting pay for work done on Shabbat – and thus a Hazan may not be paid for the work he does on Shabbat. The Shulhan Aruch then proceeds to cite an opinion that allows hiring a Hazan for Shabbat – "Ve’yesh Mi She’matir." The Mishna Berura explains that according to this view, the Sages did not apply their enactment to situations involving a Misva, and therefore a Hazan may be paid for the important religious services he performs on Shabbat. However, the Mishna Berura adds, even according to this view the Hazan is warned that he will not experience blessing from the money he earns on Shabbat.
There is a well-known rule that when the Shulhan Aruch issues a ruling, and then cites a view that disagrees with that ruling ("Setam Va’yesh"), Halacha follows the first view mentioned ("Halacha Ki’stam"). In this case, then, Halacha follows the stringent view, that it is forbidden to hire a Hazan for Shabbat. And thus although the Mishna Berura observes that the common practice was to follow the lenient position, we follow the Shulhan Aruch’s ruling, that it is forbidden to hire Hazanim.
How, then, are Hazanim hired by synagogues to lead the Shabbat services?
One answer is based on the comment of the Rama (Rav Moshe Isserles of Cracow, 1525-1572) noting that a Hazan is allowed to receive a monthly or yearly salary. Although it is forbidden to him to receive payment for his work on Shabbat, he may be paid if he is hired on a monthly of annual basis. This Halacha is known as "Habla’a" (literally, "swallowing"), and allows one to receive payment for work done over an extended period even if it includes Shabbat. Moreover, Hazanim generally have to prepare during the week to be ready to lead the services on Shabbat, and many of them must spend time training in cantorial school. They are thus allowed to receive payment as compensation for the time spent during the week preparing to serve as Hazanim. This applies as well to a Toke’a, the one who blows the Shofar in the synagogue on Rosh Hashanah. Although he may not receive payment for sounding the Shofar on Rosh Hashanah, he may be paid for the time invested beforehand preparing. For that matter, Rabbis receive a salary even though much of their work is done on Shabbat, because they spend time during the week preparing their sermons and performing other duties.
It should also be noted that even if a Hazan does not prepare during the week, it suffices if he leads the Arbit prayer service on Mosa’eh Shabbat. Once "Ata Honantanu" is recited, Shabbat is over, and the rest of the service is thus being led on a weekday. Hence, the Hazan ends up working on Sunday, and he may therefore receive payment for his services.
Summary: Although it is forbidden to receive payment for work done on Shabbat, Hazanim may get paid for their services because of the time they invest in preparation during the week, and because they often lead the services at other times, such as on Mosa’eh Shabbat.
