Is it legal to increase utility rates due to a change in provider?

I recently learned that a case is being considered in Ukraine regarding whether a change in utility service provider can lead to an automatic increase in tariffs for consumers. I'm curious: generally, if a provider changes in an apartment building, can heating or water prices be immediately raised without approval or additional reason, or must it be somehow legally justified? What should I do if I find out about such an increase only in my utility bill?