tl;dr
you're in the wrong, you don't know what ethics is, and you're being paid to be an engineer not provide philosophical guidance.
There are other answers that talk about if it is ethical or not - this answer just says "you're not informed enough to know what ethics is".
You - OP - fundamentally do not understand what "ethics" is. Ethics has a rich and varied history. A small sampling:
- "Man is the measure of all things" (Protagoras, 490-420 BC, with a surprisingly post-modern view there)
- Machiavelli (The Prince, 1532, introducing a long-awaited explanation on why leaders get a different set of ethics from commoners)
- Philippa Foot (1920-2010, introducing the now-tech-owned trolley cart dilemma, actually introduced as part of a discourse on abortion).
Saying "is it ethical" puts you in conflict and agreement with any number of people - and any number of arguments. As you can probably see from the scattered list above that there is a lot of work done in that philosophy.
So when you ask "is it ethical" you have to ask "according to which philosopher?", and if you just don't know then I'm not sure you should be thinking in terms of ethics. It is the same as if someone started trying to order their day using software design patterns, but didn't actually know any patterns, just a few names of them. You'd think they were crazy, right?
Of course, you might just be using the biblical version of ethics, which is very western of you! And that version goes something like "be good". Google had a variant of that as their motto (and alphabet now does too). Google regularly avoids paying taxes and harvests all our data, so you can see that "be good" is... whimsical at best as a philosophy. After all, "good" is a very point of view kind of thing - my good might well be someone else's evil.
So maybe you have your own set of principles, and you're saying "anything that doesn't agree with these is unethical". That's fair - and kind of brings you in line with Protagoras (and, much much later, existentialism).
And that's fine - personal ethics! Neat! The only problem is the personal bit. You're not going to really convince anyone that you're "right" when your argument is "it is literally my way or the highway, buddy". And what if your boss is an existentialist too? Oh geeze!
As I note, there are other answers that discuss the legality of this - and of course, as an existentialist you don't care about legality per-say, just about your own world view. But I'll tell you knownow that design is very hard to copyright, (pretty much impossible in Europe), and that you're (probably) not paid to provide legal, spiritual or philosophical advice. You're paid to do work given to you. I would suggest, if the company is keeping up their end (to pay you), that you keep up yours (to do the work).