there are two different contexts here(both related to cash).
the first one is about the amount. anything above 5k, in or out, needs to be explained. the source of the money and the purpose of the money. as long as it is cash, you will be asked by the clerk at the bank. they might say the reasoning is insufficient, they might block the transaction and require actual proof of what you claim or they can escalate it to the police. the larger the sum, the higher chance of trouble.
second part is the transaction itself. if it is for business purposes, like payment for︀ invoice or buying a new car for yourself, you are not allowed to use more︁ than 5k cash, the rest has to be made through bank transfer. i think this︂ used to be 10k but now it was lowered to 5k, but don't quote me︃ on that 🙂
as far as i know, this is EUs, EU-wide, anti money laundering law.︄