Job Duties: Refusing Work Based on Pervious Scope Agreed Upon

My question involves labor and employment law for the state of: Ontario, Canada

Hi there,

I started working for a startup company who sent me a contract stating that I was a "digital designer" working in the marketing department and reporting to the marketing manger. 2 months into starting I was asked to help with the product platform front end designs. I expressed that I was not an expert and that if they wanted to job done properly that they would need to hire a separate UI/UX position. They refused and I eventually agreed to help because the marketing department was fairly new and wasn't in full swing at the time. It's now 4 months later and both the UI job and Marketing job are each at a full time capacity.

My question is thus, can I be fired for now refusing the UI/UX work seeing as my contract does not specify anything to do with that position and the scope of work is way beyond what was originally agreed upon?

Keep in mind this is a multimillion dollar company in profits and can afford the new position.

Thanks for your time,

Jadon Veldman

Job Duties: Refusing Work Based on Pervious Scope Agreed Upon