On certain days (New Moon, intermediate Festival days, Festivals, Yom Kippur, and Shabbat), a fixed minimum number of people must read from the Torah—four, five, six, or seven respectively—and one may not decrease this number, but one may add additional readers to it.
בְּרָאשֵׁי חֳדָשִׁים וּבְחֻלּוֹ שֶׁל מוֹעֵד, קוֹרִין אַרְבָּעָה, אֵין פּוֹחֲתִין מֵהֶן וְאֵין מוֹסִיפִין עֲלֵיהֶן, וְאֵין מַפְטִירִין בַּנָּבִיא. הַפּוֹתֵחַ וְהַחוֹתֵם בַּתּוֹרָה, מְבָרֵךְ לְפָנֶיהָ וּלְאַחֲרֶיהָ. זֶה הַכְּלָל, כָּל שֶׁיֵּשׁ בּוֹ מוּסָף וְאֵינוֹ יוֹם טוֹב, קוֹרִין אַרְבָּעָה. בְּיוֹם טוֹב, חֲמִשָּׁה. בְּיוֹם הַכִּפּוּרִים, שִׁשָּׁה. בְּשַׁבָּת, שִׁבְעָה. אֵין פּוֹחֲתִין מֵהֶן, אֲבָל מוֹסִיפִין עֲלֵיהֶן, וּמַפְטִירִין בַּנָּבִיא. הַפּוֹתֵחַ וְהַחוֹתֵם בַּתּוֹרָה, מְבָרֵךְ לְפָנֶיהָ וּלְאַחֲרֶיהָ:
On the days of the New Moon and on the intermediate days of a Festival, four people read from the Torah; one may neither decrease the number of readers nor add to them. And one does not conclude with a reading from the Prophets. Both the one who begins the reading and the one who concludes the reading from the Torah recite a blessing. The first reader recites a blessing before the beginning of the reading, and the last reader recites a blessing after its conclusion, but the middle readers do not recite a blessing. The mishna formulates a general principle with regard to the number of people who read from the Torah on different occasions. This is the principle: Any day on which there is an additional offering sacrificed in the Temple and that is not a Festival, i.e., the New Moon and the intermediate days of a Festival, four people read from the Torah; on a Festival, five people read; on Yom Kippur, six people read; and on Shabbat, seven people read. One may not decrease the number of readers, but one may add to them. And on these days one concludes with a reading from the Prophets. Both the one who begins the reading and the one who concludes the reading from the Torah recite a blessing; one recites before the beginning of the reading and one recites after its conclusion, but the middle readers do not recite a blessing.