This is related to the removal of 'de minimis' rule that exempts parcels under $800 to ship duty free. This has caused some European postal services to stop/delay shipping some packages to the US [0]. The Dutch postal service for instance has stopped shipping to the US [1]

[0]: https://apnews.com/article/us-tariffs-goods-services-suspens...

[1]: https://www.postnl.nl/campagnes/online-frankeren-vs/