This happens all the time in business; an employee says, “I wasn’t hired to do that,” or “that’s not in my initial job description.”
The obvious solution to this is to see job roles and responsibilities as a living document that should be updated with all and any significant change. For example, I was hired at this company in a marketing role, and now I am the CEO, can I push back on the Board and say 99% of my current job is not in my job description and I’m therefore not doing it? I suppose I could say that as I was packing up my box and clearing off my desk.
There are legal protections for employees to refuse work and by and large they are associated with health & safety; but there are also protections if an employee isn’t trained or capable of doing the work. You can’t tell a carpenter to wire a house for example.
As you have described it, the employee doesn’t have standing, but before you take the axe out, think about this employees tenure; it might be advisable to have a conversation about the company’s needs, the evolving role, the new responsibilities, and what you are willing to do to make them successful. You might also want to find out the real reason they don’t want to do the task, maybe they see themselves as being set up for failure, or maybe they don’t think they can do that job well.