Why does or should a company need to pick from existing temporary workers? Perhaps they are temporary because the company doesn't believe any of the existing temps are better than what they have found? Unless there is a pattern of discrimination against a protected class, e.g. only one race was selected and all others were denied, there is nothing of which I am aware which requires any company to hire temporary workers before they hire anyone else. If there was talent they wouldn't want to leave they would likely hire the talent. If nepotism is at play there is very little that can be done except as it relates to discrimination (above) against a protected class or there is a contractual right (likely none.)