I grew up around some protestant families who believed any kind of birth control - including “natural family planning” - was wrong. See: Full Quiver Movement.
‘Course, I’m a Calvinist and think God laughs equally at any kind of birth control... what, you’re actually going to stop Him if He wants to give you a child? Not even abstinence has a 100% success rate for all of history!
I had a lengthy discussion with a theologically sound Calvinist friend of mine and his take was that it’s ok as long as it doesn’t pose a risk post-conception; IE the pill preventing a fertilized egg from implanting.