הלכה על שבת 229:1

From the laws of the commandment is that which they, may their memory be blessed, said (Megillah 7b) that anything which is forbidden to do on Shabbat - even though it is not totally work - is forbidden on Yom Kippur. The principle of the matter is, "There is no difference between Shabbat and Yom Kippur except that volitional work on Shabbat is [punishable] with stoning, and on Yom Kippur with excision." And nonetheless, they, may their memory be blessed, permitted to trim vegetables on Yom Kippur from [the time of] the afternoon service and onward, so that it will be found ready immediately on the evening [after it] - which is not permitted on Shabbat. But the people have become accustomed to be strict about the thing and to practice prohibition in the matter, as [on] Shabbat for everything. And the rest of its details are elucidated in Tractate Yoma.