Employer changed agreed schedule right after I signed offer letter- red flag ?

I recently accepted a full-time healthcare job after the schedule was discussed multiple times and included in the written offer.

An hour after I signed, they contacted me saying they wanted to change one of my regular workdays due to staffing needs. I had already made other personal and work commitments based on the schedule we agreed on.

I pushed back and explained that schedule consistency was an important part of why I accepted. They’re discussing it with leadership and getting back to me.

The offer does state that the schedule may be subject to change based on business needs. My concern is whether I should now expect additional schedule changes in the future. If the employer expects ongoing flexibility with my regular workdays, would it be reasonable to renegotiate compensation or ask for clearer schedule protections.

The job otherwise seems like a good opportunity and the pay/benefits are solid, so I don’t necessarily want to walk away over one schedule change. My concern is whether this is a sign that the employer will regularly change my schedule whenever it suits them and not me.

Would you see this as a red flag? Would you insist they honor the original schedule, offer some flexibility on alternative days, or reconsider the job altogether?