In most cases, it's perfectly fine and legal for government employees to take a second job. Some moonlighting opportunities, however, are off-limits. Most governments and government agencies ban second jobs that create a conflict of interest or interfere with your government work. Whether you're a federal, state or local government employee, find out your employer's policies before you accept any outside offers.
Conflict of Interest
A government employee's ability to work a second job depends on a number of circumstances, including the type of job. For example, suppose you work for a federal agency that pays for a research project and oversees the contractor's research. If the contractor offers you a second job, taking it would be a conflict of interest. The federal government's policy is that you can't take the job unless you recuse yourself from all related government work. If your federal superiors decide you can't fulfill your duties if you recuse yourself, you'll have to find somewhere else to moonlight. Even the appearance of a conflict of interest is unacceptable. Conflict-of-interest rules at lower levels of government follow the same general principles.
State and Local
Rules vary for other levels of government. In the state of Washington, for example, public employers can impose reasonable restrictions on second jobs. If your government job requires you to be available outside regular hours, you can't take an outside job that interferes with that schedule. In addition, many governments forbid employees from working for any contractor the government in question does business with.
Some government agencies require prior approval before employees can take a second job. For example, the U.S. Department of Agriculture requires written approval for outside jobs, but only from employees who have to file financial disclosure statements. These would include employees with a high level of authority or lower-level workers with influence over contracting or procurement.