In Knox County, they follow the civil service or merit protection law as it is written--no halfway measures.
The News-Sentinel posted an article late last night about a Knox County deputy who announced that he was running for Sheriff in Knox County and was promptly fired. Click here.
Of course, that is what the State Attorney General has repeatedly said is the law in Tennessee as it is written. Here and here.
Until someone successfully challenges the law in court, civil service in Tennessee apparently comes with a price. You get job protection with civil service, but in return you give up the right to run for public office.
And here is a link to information about the Federal Hatch Act--another law that is often mentioned when the subject of government employees running for public office comes up.