Does converting a province to a different religion lower relations with allies?

[Six-Monts]

I'm England and i adopted the Reformed religion a while ago; i'm now in the process of uniformizing my provinces' religion. Portugal is my ally and is still Catholic. My relation with them was over 100 but last time i checked it was at 0. The only thing that happened that i can see is that a couple of catholic/protestant provinces were converted to reformed. I'm guessing that converting provinces doesn't help relations, which would be totally logical considering the narrowmindness of the era. I'm just wondering what exactly is the penalty?
Thanks

 

[Icendoan]

Converting to a different religion lowers relations dramatically, from 100 to 0, as you noticed. I don't think conversion of individual provinces lowers relations.

 

[unmerged(605863)]

But converting to another relation also gives a constant relation penalty, which would explain the relation change
Idk what els did you do