According to Article 26 of the Convention implementing the Schengen Agreement and Article 13.3 of the Regulation (EU)2017/2226, before boarding transport carriers are obliged to verify that:
non-EU nationals requiring a short-stay visa have one
the number of entries authorised by their visa have not been exhausted.
As passport stamping will no longer exist once the EES is operational, carriers must use an online interface to perform these checks instead.
For more information, please check the FAQ in support of carriers