You should have gone with firefighters.
Cops famously never act in solidarity with other workers. In fact, they actively work against workers' rights.
Cops "over policing", or more accurately, "targeting", most certainly violates certain fundamental rights. A mailman not delivering packages to some company offices does not.
I would classify use of infrastructure as a right. Like if a toll booth operator refused to take money from certain people.
Also, in this case, it sounds like the workers are also not allowing anyone else to deliver the packages, so it is not just "a mailman not delivering packages to some company offices".
We aren't talking about people here. Corporations don't have that kind of consideration in most of Europe.
Call it a "boycott". It's perfectly legal and obviously not comparable to cops targeting people in the slightest.
The latter is more easily able to be used for extortion.
Similar to cops deciding not to police a region populated by a certain tribe. Or, in the same vein, over policing a certain region/tribe.