Usually, a non-Jew who is paid by the job may do work for a Jew on Shabbat, as he is considered to be working on his own behalf in order to receive the pay. However, he may not be told to do the work on Shabbat.[1] In this case, your instructions are that if the limit is reached on Shabbat, the non-Jew should make the transaction specifically then. Thus, at first glance it seems that there could be a problem with placing such an order in your case.
However, our research has shown that after one places an online order, there is rarely human intervention in its processing. When no melacha is being done on your behalf on Shabbat by a person, but only automatic computer activity occurs, the main question disappears. It is possible that someone at your brokerage will do melacha in sending you a confirmation notification or some other action. Nevertheless, even if this does happen, you presumably have not asked them to do this on the same day of the transaction, and thus you have not given instructions that someone should do work for you on Shabbat.
Furthermore, there is a much broader basis for not being concerned even when work would be done on Friday. The final bell on the NYSE is at 4:00 PM and the earliest sunset in New York is 4:28 PM. Therefore, there are no stock transactions taking place there on New York’s Shabbat.[2] The question remains, however, whether the important factor is that they do their work for you before Shabbat at their location or that the work they do for you is not done when it is Shabbat at your location.
We will start with some halachic background. The gemara[3] says that Reuven may ask Shimon to watch Reuven’s fruit that are outside of his techum Shabbat[4] but within Shimon’s techum. The Rashba[5] extrapolates from this that if Reuven accepted Shabbat early, he may ask Shimon, who did not yet accept it, to do work on his behalf. Why don’t we assert that Shimon’s action relates back to Reuven through the principle of shelichut,[6] much as we forbid a Jew to have a non-Jew do work on his behalf on Shabbat?[7]
Three answers appear in the poskim: 1) The prohibition to ask others was not instituted when there is a way in which one would not be prohibited from doing the work himself or if he had such an option in the past.[8] In the above cases, Reuven could have gone to the fruit via “burgenin”[9] or he could have not accepted Shabbat. 2) One who accepts Shabbat early does so only regarding prohibitions that he performs himself.[10] 3) Reuven may request of Shimon something that is not a forbidden melacha for Shimon based on his situation. This is different from the scenario of asking a non-Jew to do something that would be forbidden for him if he were obligated in Shabbat.[11] The third answer is the strongest and most accepted one.[12] Therefore, even if someone would be doing work for you when it is Shabbat for you, since it is not a violation of Shabbat for the one doing it, you may have him carry out the work.
One issue remains. R. Akiva Eiger[13] maintains that one may not have a transaction on his behalf take effect on Shabbat even when the practical dealings are already completed before Shabbat. Therefore, ostensibly, even though nothing is being done wrong on Shabbat, the fact that the transaction may be settled on Shabbat should be a problem. However, R. Akiva Eiger’s theory is so novel that many poskim disagree with it, and others limit it to cases similar to the contexts that are the basis of his idea. Thus, his concern need not be applied here.[14]
A final observation is of critical importance. If we were to prohibit the described trade orders on Friday because they will likely happen when it is Shabbat for the owner, then there are even stronger reasons to apply the stringency to the following situation: During the time that the owner of a kosher bakery in New York is visiting Israel, the bakery should have to close seven hours before Shabbat begins there! As several poskim point out, we have never heard of such a chumra, and we have presented ample justification above for why it is unnecessary. The same logic, obviously, can be used to permit the much less severe case of an automatic transaction on amorphous entities known as shares.