First of all, they are not "shop stewards" or have a "shop floor union meeting", for the simple reason that they are from Sweden. They are "fackliga representanter" and the went to a "facklig konferens".
You cannot and should not try to understand this from any other context than then Swedish legal an cultural one. Don't try to translate this into whatever legal and cultural context happen to come first in mind for you.
A direct translation of "facklig representant" is "union representative". This does not mean that it in any way can be compared with the situation in any other country, labor laws are different, and the way unions are set up is not the same.
There are not enough details in the sources I have seen to be able to fully identify if 100% of the participants were employed by the Swedish police (as civil servants), or if one or more were employed by the union. The unions employ specialists in different subjects, so it's not impossible that some of those joined the conference to assist the union representatives from the police organisation that was discussing the reorganisation.
And to understand why the union would discuss such a topic you need to understand what
MBL is, and why that is important in Sweden. However, I cannot see why an explanation of that has anything to do with M/S Estonia.