The norms of political activity for federal employees in the United States were set out in 1939 Hatch Act and the several subsequent amendments. After the amendments of 1993, Most federal employees are now free to engage in many types of political activities, including actively participating in partisan political management and campaigns. But they are severely prohibited from using official authority or influence to interfere with an election, knowingly soliciting or receiving political contributions, and running for public office in partisan elections. Additionally, employees are prohibited from engaging in political activity while on duty, in a government office, wearing an official uniform, and using a government vehicle. The U. S. Office of Special Counsel (OSC) and the Merit Systems Protection Board (MSPB) are authorized to ensure compliance by government employees with the Hatch Act. Regarding to the whole system, the author points out four features including: 1. Employees, according to the characteristics of positions they occupied, are subject to different extensive restrictions on political activities. 2. The costs associated with political activity may not be paid for by money derived from the Treasury of the United States. The expenses, except de minimis, incurred when the Presidential appointed employees engaged in political activity have to be reimbursed to the Treasury within a reasonable time. 3. OSC and MSPB are independent, quasi-judicial, regulatory agencies in the field of federal personnel administration. Depending on the severity of the violation, OSC will either issue a warning letter to the employee, or prosecute a violation before MSPB to seek disciplinary action. 4. An informal and flexible way, mediation, is adopted by OSC and MSPB to resolve complaints and allegations.Keywords: the United States, U.S. federal government employees, political activity, Hatch Act