Stepping down from only one aspect of my role? Telling my boss I have too much work...?

I work in a secretarial position for a large company and part of my role is to collate sales data, import that data to a spreadsheet (shared drive) and produce an employee brochure which is then passed to the Sales Secretary. I ve done this since starting in the role 7 years ago but around one year ago the Sales... show more I work in a secretarial position for a large company and part of my role is to collate sales data, import that data to a spreadsheet (shared drive) and produce an employee brochure which is then passed to the Sales Secretary.
I ve done this since starting in the role 7 years ago but around one year ago the Sales Secretary position was taken over by another colleague. My role as a whole is vast and this sales side of things is relatively small however the Sales Secretary treats me like her personal secretary. She will ask me for data "immediately" which can easily be pulled from the shared drive and although not holding a higher ranking position she will treat me as a subordinate.
I have a meeting with my line manager and intend to ask if I may step down from this aspect of my role. There is more than enough other work and I am happy to take a pay-cut.
How is best to present my case?
3 answers 3