A. Emoluments Clause
The Emoluments Clause of the United States Constitution (Article 1 § 9, clause 8) prohibits Federal employees from engaging in any employment with a foreign government or the political subdivision of a foreign government, including a public university or a commercial enterprise owned or operated by a foreign government. This prohibition does not apply to a foreign privately-owned corporation or an international organization, such as the International Atomic Energy Agency.
B. Foreign Gifts and Decorations Act
The Foreign Gifts and Decorations Act (5 USC 7342) prohibits Federal employees from accepting a gift exceeding $350 in value from a foreign government. This prohibition includes an international organization, such as the IAEA. A prohibited gift even includes travel expenses exceeding $350 in value, unless the travel takes place entirely outside the United States. The restriction also extends to the employee's spouse and dependents. Employees can accept travel and travel-related expenses from a foreign government for activities taken on behalf of that government as part of official duties.