Fifa rules state only that a club must inform another of its intention to speak to their player. The Premier League goes a significant step further by maintaining that written consent must be obtained.
A club can approach the player only “with the prior written consent of the club to which he is contracted,” rule T.1.2. of the latest Premier League handbook says.
The same goes for agents hawking their players to other clubs. By the book, they cannot do so “without having obtained the prior written consent of his club” – rule T.6.
And even discussing it publicly is forbidden, rule T.8. specifying that “a statement made publicly by or on behalf of a club expressing interest in acquiring the registration of a contract player or by a contract player expressing interest in transferring his registration to another club shall in either case be treated as an indirect approach”.
The Premier League successfully took action against Liverpool, Manchester City and Everton in 2017 and 2018 regarding the tapping up of academy footballers (it’s incredibly weird to tap up an 11-year-old, but there you go), issuing fines and academy transfer bans.
But it still happens, and when it comes to first teams its even harder to find solid modern examples. You can cite a handful of cases, at Chelsea, Roma, Sion, a few others.
The action-taken-to-offence-committed ratio make it barely worth the time taken to write the rules.