When you partner with a PEO, the PEO may use its own EIN for certain tax purposes, particularly payroll taxes. However, you retain your company's EIN for other business matters. This arrangement, known as a "co-employment" relationship, allows the PEO to leverage its size for better benefits and rates. The specific arrangement can vary depending on the PEO and services provided, so it's important to clarify this with any PEO you're considering.