Every UUA congregation is a “church” under U.S. tax law and therefore has Tax Exempt Status. If you have property rentals, a church store, or other Unrelated Business Income, that might be taxable and you should consult a tax professional.
UU Congregations are responsible for remitting Payroll Taxes for all employees. Keep in mind that ministers have “dual-tax” status, so the congregation does not pay FICA for ministers.