All employment and self-employment creditable for Social Security purposes, except in a few employment situations (e.g., religious orders under a vow of poverty, foreign affiliates of American employers), or the employer must elect state and local government coverage. However, as of July 1991 coverage became mandatory for state and local employees who do not participate in a public employee retirement system. All new state and local employees have been covered by Social Security since April 1986 except ministers or self-employed members of certain religious groups who can opt out of coverage. Covered employment for hospital insurance includes all federal employees, whereas covered employment for the Old Age, Survivors, and Disability Insurance (OASDI) Program includes some, but not all, federal employees.