All participating countries in the European Championship next summer may select 26 players.
UEFA decided on Tuesday to allow three extra players due to the corona virus.
With this, UEFA wants to prevent countries from getting into trouble if some corona infections are detected within the national team.
The match selections will continue to consist of 23 players during the European Championship.
As a result, three players will have to sit in the stands, if everyone is fit.
Each country has the right to substitute injured players for a fit player before its first match.
This also applies to players who have tested positive for the corona virus during the upcoming European Championship, or if a player is obliged to be quarantined because he has been in close contact with an infected person.
The Dutch will start preparations on May 21
The European Championship starts on June 11 with the match between Italy and Turkey in Rome.
Exactly a month later the final will be played in Wembley in London.
The Orange team will complete its first training session on 21 May in the run-up to the European Championship. Players who have club obligations are not yet present. The team of national coach Frank de Boer will play friendly against Scotland (June 2) and Georgia (June 6), before the first group match against Ukraine is scheduled for 13 June.