The Hatch Act of 1939

The Hatch Act was created as an act to "Prevent Pernicious Political Activities" following the allegations that "Democratic Party politicians used employees of the WPA during the congressional elections of 1938"
New Mexico representative Sen. Carl Hatch sponsored this Act in 1939, until it was signed by President FDR.

The Hatch Act restricts and limits "certain political activities of Federal employees both on and off duty"

Political Activity = something in active support of or opposition to a political party, a candidate for partisan political office , or a partisan political group

Federal Employees May Not

• Engage in political activity while using a Government vehicle
• Solicit, accept, or receive political contributions from a subordinate employee 
• Wear political buttons
• Engage in political activity while using Government property
•  including computers, printers, copiers, fax machines, and telephones 

In "United Public Workers vs. Mitchell (1947)" the U.S. Supreme Court held, in a 4-3 ruling, that the Hatch Act of 1939 did not violate the 1st, 5th,9th,or 10th amendment.

Originated in the District of Columbia and, when appealed, went directly to the Supreme Court
Federal Service employees claimed the Hatch Act violated their 1st amendment right to free speech by prohibiting them from taking part in political campaigns.

http://www.archives.gov/legal/ethics/hatch-act.html

http://www.washingtonpost.com/blogs/the-fix/wp/2014/07/17/do-you-work-in-go...

http://www.dod.mil/dodgc/defense_ethics/resource_library/hatch_act_q_a_less...

http://supreme-court-cases.findthebest.com/l/50/United-Public-Workers-Of-Am...