In applying for a job with a heating and air conditioning company, an applicant stated that he had been laid off from his previous job. But the truth was that the applicant, Michael Starnes, already had a job, he was a paid union organizer (a "salt") who took a leave of absence to get a job at the heating company and help organize its staff.
After learning that Starnes lied on his application about his status as a salt, the company fired him. Starnes filed a charge with the National Labor Relations Board (NLRB).
Employers can't refuse to hire somebody simply because he is a salt. The Supreme Court declared this in 1995. But the question left open, and the question here, is whether a salt may lie to get a job.
The NLRB's answer was a resounding "yes." And the 7th Circuit Court of Appeals agreed. Bottom line: The lie about the other job doesn't matter: An employer can't turn down a qualified job applicant merely because he's a salt. (Hartman Bros. Heating & Air Conditioning Inc. v. NLRB, No. 01-1321, 7th Cir., 2002)
Advice: To prevent union salts from infiltrating your workplace, consider adopting a hiring policy that states: "No one will be hired who is employed by another employer and who intends to keep that employment after starting with this company. Anyone who has a second job or moonlights while employed here is subject to immediate termination."
To be an effective weapon, your hiring policy must be consistently enforced. That means you have to take a tough stance with all secondary employment, not only secondary employment for a union. As much as you'd like to have flexibility when it comes to allowing workers to moonlight, you'll be in a much stronger position of closing the door on salts if you consistently ban second jobs.
Finally, regardless of whether a new hire is a salt, you can fire him for lying about job qualifications.