Daat HaRav — The Shulchan Aruch of the Alter Rebbe on Siman שמ"א

הֶתֵּר נְדָרִים בְּשַׁבָּת וּבוֹ ד' סְעִיפִים:

מַתִּירִין נְדָרִים בְּשַׁבָּת אִם הֵם לְצֹרֶךְ הַשַּׁבָּת, כְּגוֹן שֶׁנָּדַר שֶׁלֹּא לֶאֱכוֹל בָּשָׂר אוֹ שֶׁלֹּא לִשְׁתּוֹת יַיִן, אוֹ שֶׁנָּדַר מִמַּלְבּוּשׁ הַצָּרִיךְ לוֹ הַיּוֹם, וַאֲפִלּוּ הָיָה לוֹ פְּנַאי לְהַתִּירָם קֹדֶם הַשַּׁבָּת — מֻתָּר. אֲבָל נְדָרִים שֶׁאֵינָם לְצֹרֶךְ הַשַּׁבָּת — אֵין מַתִּירִים בְּשַׁבָּת, אֲפִלּוּ לֹא הָיָה אֶפְשָׁר לְהַתִּירָם קֹדֶם הַשַּׁבָּת.

אֲבָל הַבַּעַל יָכוֹל לְהָפֵר נִדְרֵי אִשְׁתּוֹ אֲפִלּוּ שֶׁאֵינָם לְצֹרֶךְ הַשַּׁבָּת, וְכֵן הָאָב לְבִתּוֹ, לְפִי שֶׁאִם לֹא יָפֵר לָהּ "בְּיוֹם שָׁמְעוֹ" — לֹא יוּכַל עוֹד לַהֲפִירָם:

Annulment of vows (hatarat nedarim) on Shabbos, containing 4 seifim:

One annuls vows on Shabbos if they are for the need of Shabbos — for example, one who vowed not to eat meat or not to drink wine, or who vowed against a garment he needs on that day — and this even if he had leisure to annul them before Shabbos: it is permitted. But vows that are not for the need of Shabbos — one does not annul them on Shabbos, even if it was not possible to annul them before Shabbos.

However, the husband can annul his wife's vows even when they are not for the need of Shabbos, and so too a father for his daughter, since if he does not annul them for her "on the day he hears" — he will no longer be able to annul them:

מִי שֶׁנִּשְׁבַּע לַעֲשׂוֹת מְלָאכָה פְּלוֹנִית עַד זְמַן פְּלוֹנִי וְלֹא נִזְדַּמֵּן לוֹ לַעֲשׂוֹתָהּ עַד יוֹם הָאַחֲרוֹן שֶׁל אוֹתוֹ זְמַן, וְאוֹתוֹ יוֹם בָּא בְּשַׁבָּת וְאִי אֶפְשָׁר לַעֲשׂוֹתָהּ בְּשַׁבָּת, וְיֵשׁ לוֹ פְּתָחִים לְהַתִּיר נִדְרוֹ מִשְּׁבוּעָתוֹ — מַתִּירִין לוֹ אֲפִלּוּ בְּשַׁבָּת, מִפְּנֵי שֶׁאִם לֹא יַתִּירוּ לוֹ הַיּוֹם — אִי אֶפְשָׁר לְהַתִּירוֹ לוֹ לְמָחָר:

One who swore to perform a certain melachah by a certain time and did not have the opportunity to perform it until the last day of that period, and that day falls on Shabbos when it is impossible to perform it, and he has pesachim (openings — pretexts) to annul his vow or his oath — they annul it for him even on Shabbos, because if they do not annul it for him today — it will be impossible to annul it for him tomorrow:

הַתָּרַת חֲרָמִים דִּינָהּ כְּהַתָּרַת נְדָרִים, וְאֵין מַתִּירִין אֶלָּא לְצֹרֶךְ הַשַּׁבָּת. אֲבָל נָהֲגוּ לְהַתִּיר חֶרְמֵי הַקָּהָל אֲפִלּוּ אֵינָם לְצֹרֶךְ הַשַּׁבָּת, לְפִי שֶׁאֵין דֶּרֶךְ לִהְיוֹת כְּנוּפְיָא אֶלָּא בְּשַׁבָּת, וְאִם לֹא יַתִּירוּהוּ בְּשַׁבָּת — לֹא יִתְאַסְּפוּ בְּיוֹם אַחֵר, וְנִמְצָא שֶׁאֵין לוֹ הֶתֵּר לְעוֹלָם.

אֲבָל אֵין מַחֲרִימִין בְּשַׁבָּת כִּי אִם מִדָּבָר שֶׁהוּא לְצֹרֶךְ שַׁבָּת, וְכֵן לְמִי שֶׁחִלֵּל שַׁבָּת, אֲבָל לֹא לְמִי שֶׁעָבַר עֲבֵרָה אַחֶרֶת.

אֲבָל דָּבָר שֶׁיֵּשׁ בּוֹ תִּקּוּן הַמְּדִינָה, וְאִם לֹא יַחֲרִימוּ בְּשַׁבָּת לֹא יִתְאַסְּפוּ בְּיוֹם אַחֵר וְיִגְרַע הַתִּקּוּן — אֲזַי מֻתָּר לְהַחֲרִים, כְּמוֹ שֶׁמֻּתָּר לְהַתִּיר הַנֶּדֶר אוֹ הַחֵרֶם מִטַּעַם זֶה. וְלָכֵן אֵין לִמְחוֹת בְּמַה שֶּׁנָּהֲגוּ בִּירִידִים שֶׁהַשַּׁמָּשׁ קוֹרֵא מִתּוֹךְ הַכְּתָב מִי שֶׁהוּא מֻחְרָם עַל פִּי בֵּית דִּין מִשּׁוּם חוֹבוֹתָיו, מִפְּנֵי שֶׁצָּרִיךְ לְהַכְרִיז בְּשַׁבָּת שֶׁמִּתְאַסְּפִים כֻּלָּם וְיוֹדְעִים לְכֻפּוֹ בְּעִירוֹ לְשַׁלֵּם, וְלוּלֵי זֶה הָיוּ נִפְסָדִין הַחוֹבוֹת וְכָל מַשָּׂא וּמַתָּן.

וְכֵן מִי שֶׁבִּזָּה הֶחָכָם — יָכוֹל לְנַדּוֹתוֹ לִכְבוֹדוֹ, מִפְּנֵי שֶׁזֶּהוּ גַם כֵּן תִּקּוּן הַמְּדִינָה לְהַעֲמִיד הַמִּשְׁפָּט עַל תִּלּוֹ, וְגַם דְּבַר מִצְוָה הוּא מִשּׁוּם כְּבוֹד הַתּוֹרָה.

וְאֵין צָרִיךְ לוֹמַר שֶׁמֻּתָּר לְהַחֲרִים בְּשַׁבָּת בְּדָבָר הַנּוֹגֵעַ עַל הַכְּלָל, כְּמוֹ שֶׁהֶחֱרִימוּ בְּשַׁבָּת אֶת הָעוֹסְקִים בְּסִפְרֵי הַטֶּבַע כָּל יְמֵיהֶם:

The annulment of charamim (bans, excommunications) follows the same law as the annulment of vows: one annuls only for the need of Shabbos. But the custom is to annul communal charamim (chermei haqahal) even when they are not for the need of Shabbos, since it is not customary to be in assembly except on Shabbos, and if they do not annul it on Shabbos — they will not gather on another day, and it turns out that he will never have any release.

But one does not pronounce a cherem on Shabbos except for something that is for the need of Shabbos, and likewise against one who has profaned Shabbos — but not against one who has transgressed another sin.

However, a matter that involves the tikkun hamedinah (welfare of the community), and where if they do not pronounce the cherem on Shabbos they will not gather on another day and the welfare will be diminished — then it is permitted to pronounce the cherem, just as it is permitted for this same reason to annul the neder or the cherem. Therefore one should not protest the practice that has been established at fairs whereby the shamash (beadle) reads from a written list those who have been placed under cherem by ruling of the beis din on account of their debts, since it must be proclaimed on Shabbos when all gather and know how to compel him in his city to pay; for were it not for this, the debts and all commerce would be ruined.

So too one who has degraded the chacham (sage) — one may excommunicate (lenadot) him for his honor, since this too is tikkun hamedinah, namely to uphold justice in its proper place, and it is also a matter of mitzvah on account of the honor of the Torah.

And it goes without saying that it is permitted to pronounce a cherem on Shabbos on a matter affecting the community — as for instance they placed under cherem on Shabbos those who engage all their days in books of natural philosophy (sifrei hateva):

מִי שֶׁנִּדּוּהוּ בַּחֲלוֹם — מַתִּירִין לוֹ בְּשַׁבָּת:

One whom they excommunicated (nidduhu) in a dream — they release him on Shabbos: