Responsa for Sheviit 10:1

שְׁבִיעִית, מְשַׁמֶּטֶת אֶת הַמִּלְוָה בִּשְׁטָר וְשֶׁלֹּא בִשְׁטָר. הַקָּפַת הַחֲנוּת, אֵינָהּ מְשַׁמֶּטֶת, וְאִם עֲשָׂאָהּ מִלְוָה, הֲרֵי זֶה מְשַׁמֵּט. רַבִּי יְהוּדָה אוֹמֵר, הָרִאשׁוֹן הָרִאשׁוֹן מְשַׁמֵּט. שְׂכַר שָׂכִיר, אֵינוֹ מְשַׁמֵּט, וְאִם עֲשָׂאוֹ מִלְוָה, הֲרֵי זֶה מְשַׁמֵּט. רַבִּי יוֹסֵי אוֹמֵר, כָּל מְלָאכָה שֶׁפּוֹסֶקֶת בַּשְּׁבִיעִית, מְשַׁמֶּטֶת, וְשֶׁאֵינָהּ פּוֹסֶקֶת בַּשְּׁבִיעִית, אֵינָהּ מְשַׁמֶּטֶת:

The Sabbatical year cancels a loan [that was made] with a contract and [a loan that was made] without a contract. Store credit is not cancelled, but if it was made into a loan, it is canceled. Rabbi Yehudah says, the previous [of each subsequent purchase on credit] is cancelled. Wages owed to a worker are not canceled, but if it was made into a loan, it is canceled. Rabbi Yossi says, any type of work which must pause during the Sabbatical year, [wages owed for that work] are cancelled. But any work which need not pause during the Sabbatical year, [wages owed for that work] are not canceled.

Teshuvot Maharam