Translate the following English sentence to French:
"At the moment, in services which are not theoretically liberalised - as is the case with national postal services - there is a basic form of liberalisation, which is agreed within the framework of the Universal Postal Union, allowing for lower tariffs."
Actuellement, dans des services théoriquement non libéralisés - comme les services postaux nationaux -, il existe une libéralisation fondamentale, qui se développe à travers le système de l' Union postale universelle permettant des tarifs bas.