You have employees on payroll
Workers' compensation stops being optional at a headcount threshold set by your state, and it is priced off payroll: a rate per hundred dollars of payroll for each job classification, multiplied by your experience modifier. Two things follow from that. The classification codes on your policy matter more than the premium quoted at the start of the year, because the wrong code can be wrong by a factor of several. And the policy is audited after the term ends, so the number you pay is the number your actual payroll produced, not the estimate. Having employees at all also creates employment-practices exposure — the claims that come from hiring, firing, promoting, and managing people.