Teams will be allowed to select a 26-player squad instead of the usual 23 at this summer’s European Championship.
The change has been implemented to lessen the load on players after a club season compressed because of the coronavirus pandemic.
It will also help managers adapt if outbreaks occur during the tournament.
The decision, taken by Uefa’s national teams committee in April, was approved by Uefa’s executive committee on Tuesday.
In a statement, it said the rules were approved “in order to guarantee the smooth running and continuity of the competition in light of the Covid-19 pandemic”.
A rule allowing each team to make up to five substitutes per game had already been confirmed.
However, 23 players will remain the maximum number permitted on team sheets for matches.