It's encoded in the CE rule 561/2006 article 7:

https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CEL...

  Article 7
  
  After a driving period of four and a half hours a driver shall take an uninterrupted break of not less than 45 minutes, unless he takes a rest period.
  
  This break may be replaced by a break of at least 15 minutes followed by a break of at least 30 minutes each distributed over the period in such a way as to comply with the provisions of the first paragraph.