Depends on the employment law of the country in which your contract relates to, and what is written within that contract. My contract explicitly states I can be expected to fly any aircraft type, but the employer would provide the rating. In the U.K. for instance, your employment contract cannot legally be changed without your agreement. If the new aircraft type is replacing your current type, I’d say they’d either have to make you/your role
redundant, or offer you the rating with/without a bond, then the choice is down to you.