Ex suddenly wants to change custody schedule after 2 years

So my ex texts me out of the blue saying she needs to swap weekends every other month because of her new job. We've had the same schedule for 2 years and the kids are doing great with it. I'm worried this is going to confuse them and mess up their routine. Do I have to agree to this? Should I talk to my lawyer first or just try to work it out with her? This feels like it keeps happening where she changes things without really considering how it affects the kids.