How do I become eligible for COBRA? Does it matter if I switched to part-time or was fired, or is it any time I lose employer coverage?
In general, if you have been enrolled in health insurance for at least one day and then lose coverage for due to losing full-time status or due to termination, you qualify for COBRA. This is true even if you elect to go from full-time to part-time or are fired.
The above applies to Federal COBRA and employers with over 20 FTE. The exception to the rule is that if you work for an employer with under 20 Full-time Equivalent Employees (FTE), then rules for state COBRA rules apply. State COBRA rules may differ, for example the length you need to have COBRA differ by state.
For a detailed breakdown of COBRA rules, see Zenefits "Eligibility for COBRA."