One may not engage in commerce on Shabbat. One who opens his store, buying and selling on Shabbat just as he does on weekdays, negates a Torah commandment. This prohibition applies even if he is careful to avoid transgressing any of the 39 melakhot. The Torah commands that Shabbat be a “shabbaton” (Shemot 31:15), a complete cessation. One who does business in his store is not resting (Ramban, Vayikra 23:24; Ritva; Ĥatam Sofer). Neĥemia faced this problem when he arrived in Jerusalem and found that people were holding a market day on Shabbat. He recounts:
Tyrians (merchants) who lived there brought fish and all sorts of wares and sold them on Shabbat to the Judahites in Jerusalem. I censured the nobles of Judah, saying to them, “What evil thing is this that you are doing, profaning Shabbat day! This is just what your ancestors did, and for it God brought all this misfortune on this city; and now you give cause for further wrath against Israel by profaning Shabbat!” (Neĥemia 13:15-18)
As a result, the merchants began selling their goods outside the city walls on Shabbat. In response, Neĥemia ordered that the gates of the city be closed over Shabbat. “Once or twice the merchants and the vendors of all sorts of wares spent the night outside Jerusalem, but I warned them, saying, ‘What do you mean by spending the night alongside the wall? If you do so again, I will lay hands upon you!’ From then on, they did not come on Shabbat” (ibid. 19-21).
The Torah prohibition on commerce applies to one who regularly does business on Shabbat. However, one who buys or sells on Shabbat occasionally still transgresses the words of the prophets, as Yeshayahu said: “if you honor it, and not go in your own way, nor look to your affairs, nor speak of them” (58:13), and the Sages explained this to mean that one should not deal in mundane matters on Shabbat (Shabbat 113a).
It should be noted that those verses do not record a prohibition on buying and selling for the sake of a mitzva. Nevertheless, as a safeguard, the Sages prohibited all business dealings, even in service of a mitzva, out of concern lest one write (Rashi and Tosafot, Beitza 37a; MB 306:11). The only exception to this prohibition is the mitzva of settling the land of Israel, for which one may purchase land from a non-Jew on Shabbat. The non-Jew should write the contract and take the money on his own (SA 306:11; Eliya Rabba ad loc. 22; Mor U-ketzi’a; as opposed to MA ad loc. 19; see above 9:12).
Some are stringent and do not sell aliyot on Shabbat, because of the prohibition of doing business on Shabbat. However, many are customarily lenient, and they have grounds for their leniency. This is because, in this case, there is no acquisition (kinyan) or payment on Shabbat, and the assumption of the obligation to pay for the aliyot is deemed to be for the sake of a mitzva (MB 306:33; Yeĥaveh Da’at 2:41). However, if the synagogue’s income from this practice is minimal, it is improper to be lenient and waste the congregation’s time.