Also known as Labour Day. Which is a bad name, as every day of the year there are babies born! Ho ho!
In Sweden, as in most countries (I think) this is on May Day. Today. In Sweden this public holiday is usually referred to as "Första maj" = May 1st. E.g. political demonstrations on this day are usually referred to as "May 1st demonstrations". The date's special value has a way longer history, but that is usually forgotten.
I've never participated in any May 1st demo. But it was just a few years ago I realised how absurd it is that Social Democratic Party, whose demos are usually the biggest, actually have demonstrations when they are in power. As they been for the most of the last hundred years. That's socialism. Parades from the party in charge. Obviously it is about mobilization, but I still find it quite absurd. That it took me so many years to even see this is a witness to how socialist propagandised we are, or used to be. At least us who never were part of an opposition party.
The demos are not what they used to be in size, at least not for the Social Democrats. Have no idea about the various communist demos.