What step should taken to maintain security if an employee is terminated?

It can largely depend on how large the company is. In today's day and age, immediately upon being notified of their termination, the terminated employee is often escorted back to their work area and, while observed by a supervisor or security, allowed to collect their personal belongings, they then must surrender any company property entrusted to them (keys, ID cards, passcards, company-issued clothing, etc) before being escorted from the building and advised not to return. The employer will usually change any computer access codes or other confidential information the former employee may have had access to.