Siman 23

It is permitted to enter a cemetery while wearing tzitzit, provided that they do not drag over the graves. But if they drag over the graves—it is forbidden due to "mocking the poor." This is proven in Berakhot (18a). And even though with tefillin it is forbidden to enter when they are revealed, as will be explained in siman 45, and with tefillin dragging is not applicable—tefillin are different because their essence is only for the mitzvah, and there is the issue of "mocking the poor." But the tallit is a mere garment, and the Torah required one to place tzitzit upon it. Therefore, there is no issue of "mocking the poor" unless they drag over the graves. But otherwise—it is permitted.

Therefore the Rishonim wrote that this was specifically in the time of the Shas, when they would place tzitzit on garments that they wore for their own needs. But our tallitot, which are only for the purpose of the mitzvah—their law has returned to being like tefillin. And even if they are not dragging—it is forbidden. And specifically when they are revealed it is forbidden with tefillin, and likewise with a tallit when it is covered—it is permitted. Therefore, one does not need to remove the tallit katan when he goes to a cemetery, for it is under his clothes. And likewise the tallit when he wears an upper garment over it—there is no concern in the matter. And just as the law is in a cemetery, so too one who enters within four amot of a corpse or of a grave—his law is like in a cemetery. And this law has already been explained in Yoreh Deah siman 367. (And it requires further study regarding the grave or corpse of a minor, and some say there is no difference. And for me, it requires further study.)

There are those who are accustomed to tie the two tzitzit of the corners with one another when entering a cemetery. But they have achieved nothing with their remedy, for through this the tzitzit are not nullified. For it is not a permanent knot, as one will untie them immediately. Furthermore: if so, according to their reasoning, they are walking without tzitzit. Furthermore: according to their reasoning, there is a concern in this of "make it, and not from that which is already made" (see Magen Avraham, subsection 1).

Our teacher, the Beit Yosef, wrote in section 4 that in a place where they are accustomed to remove the tzitzit from the tallit of the deceased in the house, if the pallbearers wear tzitzit—there is a concern regarding them because of "mocking the poor." Thus far his words. And it implies that in a place where they are not accustomed to remove them—there is no concern of "mocking the poor," for on account of the distinction that this one is alive and this one is dead—there is no "mocking the poor." And it is not similar to a cemetery, where there is "mocking the poor" even in places where they do not remove the tzitzit from the tallitot of the deceased, as is explained from his words in Yoreh Deah siman 351, for since this person has recently died—there is not as much mockery in this as there is in a cemetery. Nevertheless, the consensus of the great authorities is that even when they do not remove the tzitzit—the pallbearers should not walk with revealed tzitzit. And there are further laws regarding this, and it has been explained in Yoreh Deah ibid.