Some firms are forbidding employees to smoke at any time, even within their own homes on their own time. To enforce such draconian policies, they are testing employees for evidence of tobacco use. This is a direct violation of the 4th Amendment to the US Constitution:
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
- Fourth Amendment to the United States Constitution