Although one may do work on Erev Shabbos until the time to be mentioned below, he nevertheless is to prepare for Shabbos prior to this time, as explained in the previous chapter and as is evident from the story told by Rav Yehuda Hachasid.
The reason: As the sages desired that from this time and onwards one is free from his duties so he can deal with his Shabbos needs. (Even if one does not need to prepare for Shabbos at all, it still remains forbidden for him to do work from Mincha and onwards as the Sages did not want to differentiate in their decree.)
If one transgresses and does forbidden work pass the above mentioned time: One who does forbidden work after Mincha will not see blessing from that work which was done. However one is not punished for doing work past this time, neither through excommunication or lashes although this is usually done for one who transgresses a Rabbinical command. Nevertheless he is to be admonished, and forcibly prevented from doing the work.
When is considered the “time of Mincha”: It is disputed as to whether the prohibition of doing work past Mincha refers to Mincha Gedola [i.e. half hour past midday] or Mincha Ketana [i.e. 3.5 minutes past midday]. Practically one who is lenient to do work up until Mincha Ketana does not lose any blessing from the work done. [The above hours are calculated in accordance to Shaaos Zmaniyos, in which one divides the total amount of day hours by 12 in order to calculate the amount of each hour.]
Stopping the people from work from after Mincha Ketana: A messenger is to be sent in order to stop the working people from doing work [of physical labor], beginning from Mincha and onwards, which is two and half hours before Shabbos.
 That one is to prepare for Shabbos in the morning.
 The Sefer Chasidim  [brought in Kaf Hachaim 251/4] writes how a woman was severely punished for having spent her time on Erev Shabbos sewing instead of preparing for her Shabbos needs. The Kneses Hagedola explains on this that although the woman had done the sewing prior to midday, she was nevertheless punished as due to this she refrained from preparing properly for Shabbos. He then explains that one is required to prepare his Shabbos needs even before the time of Mincha and the prohibition to do work after Mincha was made even when one has already completed all his Shabbos preparations.
 251/1. See Aruch Hashulchan 251/4 who brings a Limud Zechus for those which are not careful in this set of laws and continue to work past the prohibited mentioned time.
 The wording of some Poskim [Michaber and others] does not mention a prohibition but rather simply states that work past Mincha will be fruitless. Admur [as does other Poskim] however rules that it is an actual prohibition. [See Kaf Hachayim 251/7]
 The forms of work which remain permitted will be discussed below.
 The Reishis Chachmah writes based on the Zohar that after going to Mikveh, which is likened to accepting Shabbos, one is forbidden to do any work with exception to work done in preparation for Shabbos, and rather one is to spend his time learning Torah. [Kaf Hachayim 151/3]
 See above footnote in story with Rav Yehuda Hachasid, in which the Kneses Hagedola explains on this that one is required to prepare his Shabbos needs even prior to the time of Mincha and the prohibition to do work after Mincha was made even when one has already completed all his Shabbos preparations. However see Aruch Hashulchan 251/4 suggests as a defense for those which are lenient to do labor past Mincha, being that their wives prepare for them all their Shabbos needs.
 This means that whatever profit he has gained from the work done, he will accordingly lose out that same amount on a different occasion. [Ibid]
 As the Sages were not that strict regarding this prohibition. [Ibid]
 251/2; Both opinions are brought by the Michaber in 251/1.
 Mincha Gedola begins from 6 hours and 30 minutes into the day, which is a half hour past midday. [ibid] This opinion of Mincha Gedola is the opinion of Mordechai and Tur, and so rules the Bach and Levush.
 Mincha Ketana begins from 9.5 hours into the day, which is 2.5 hours prior to sunset. [ibid] This opinion of Mincha Ketana is the opinion of Rashi.
 As by a dispute in a Rabbinical matter one may be lenient. [ibid]. So rules Taz 251/1. However the Magen Avraham 251/4 plainly sides like the opinion that it refers to Mincha Ketana [and thus according to him there is no need to be stringent, unlike the implication from the wording of Taz/Admur which would hold that one that is stringent has what to be stringent on]. To note that Admur plainly rules like the lenient opinion in 256/1, which is brought next regarding the community announcement of stopping to do work. However see footnote there.
The Ketzos Hashulchan [69/6] plainly rules in accordance to the opinion which holds of Mincha Ketana, which is 2.5 hours prior to sunset, and does not mention any need to be stringent if one wishes to.
 Mishneh Berurah 251/3
 Thus we see here that Admur rules plainly like the lenient opinion. However one can answer that in truth Admur only holds this way with regards to sending messengers, as one cannot force the community to keep a stringency. However for an individual, there is room to be stringent if he so chooses. [See Magen Avraham 251 4 for a similar explanation regarding the day workers who would work until close to sunset.]