If a player has land tax and I have more lands than they do, the “you may” is what we are debating about he says it’s a choice and he doesn’t need to look for a land I say since I do have more lands he does
Someone help
The wording on the card is pretty clear. "You may" offers a choice. The choice is whether or not to search. If they decline the search, they simply choose not to do it so they don't search and they don't shuffle. As mentioned above, even if they do search, they aren't required to find anything anyway, though they would shuffle in that case.
There are three places in Land Tax's ability where a player need not find exactly "three basic land cards":
"you may": This indicates that the search is optional and the choice of whether to search is made when the ability resolves, "regardless of whether [the ability's] controller intends to exercise the ability's option or not" (C.R. 603.5). In general, however, if that player makes such a choice in advance, they will be bound to that choice unless another player intervenes (C.R. 725.2a-c; for sanctioned tournaments, see M.T.R. 4.2).
"up to three": "Up to three" means zero, one, two, or three (C.R. 107.1, 107.1b; see also C.R. 107.1c).
Because the ability speaks of searching a hidden zone (here, a library [C.R. 400.2]) for cards with certain characteristics (here, "basic land cards"), the player "isn't required to find some or all of those cards even if they're present in that zone" (C.R. 701.19b). Compare Land Tax with Diabolic Tutor or Behold the Beyond, where exactly one or three cards, respectively, have to be found, or as many as possible (C.R. 609.3; see also C.R. 701.19d), since neither spell requires searching for a particular kind of cards, but compare the latter two spells with Sadistic Sacrament, where up to three or up to fifteen cards, as the case may be, have to be found.
However, if the player chooses not to search this way, then they don't shuffle their library (because the ability uses the form "...you may search ..., then shuffle...") (see also this thread). But if they do choose to search this way, then they shuffle their library regardless of whether they choose to find no basic land cards or whether basic land cards are present in that library (C.R. 701.19g, 701.19b).
EDIT (Dec. 29, 2021): Some rules were renumbered in the meantime. Clarification.
Someone help
However, if the player chooses not to search this way, then they don't shuffle their library (because the ability uses the form "...you may search ..., then shuffle...") (see also this thread). But if they do choose to search this way, then they shuffle their library regardless of whether they choose to find no basic land cards or whether basic land cards are present in that library (C.R. 701.19g, 701.19b).
EDIT (Dec. 29, 2021): Some rules were renumbered in the meantime. Clarification.