At the place I work all us secretaries have to do a share of covering the reception desk when the receptionist is on breaks. However in the last few months I've been asked to cover a lot of half days and hours here and there. I finally reached boiling point today and told my boss I feel I'm being taken for a mug, I'm not a receptionist, I don't like doing reception, and if I did wouldn't I have applied for a receptionist job? The fact that my boss keeps volunteering me for it makes me feel completely undervalued. I'm doing far more of it than anyone else.

Am I within my rights to refuse to do it?