Employer not deducting SSN and Medicare taxes

[ceherr]

My H1-B kicked in October 2023. Ideally, that should have called for SSN and Medicare tax deductions. However, that's not the case. There have been no such tax deductions till date.

What happens now? Who is at fault here - me or my employer? Do I need to state this to my employer? If I do, will I end up paying more tax for the last year too, along with forthcoming deductions https://9apps.ooo/?

Appreciate any insights.