I was hired about two years ago to perform tasks requiring skill A. In the mean time I've spent a lot of my free time outside of work to learn skill B, as a hobby.
From what I know skill B is much more valuable in the market, and people hired to do it earn a lot more than me. But I'm happy with my current job and with skill B being only a hobby.
Somehow my boss found out that I know skill B and now wants me to start doing projects that require it, without raising my salary. Can I refuse without quitting my job? What are my options?
EDIT: Thanks for all the answers. I probably wasn't clear enough that I don't want to make skill B my career, and that's why I'm looking for way out of this situation.

without raising my salarypart: you (a) asked for a raise and he refused it or (b) he simply didn't offer a raise ? – Radu Murzea Nov 16 '17 at 21:08