If you want to work for or with the military, a military agency or a cleared contractor for the federal government, chances are you will need a security clearance. Likewise, if you work for one of these types of organization you might have your security clearance reviewed or revoked. In any event, if you are denied or your security clearance is revoked you have an opportunity to respond and provide any mitigating evidence. You have a right to administrative hearing. Administrative hearings require the need for a lawyer.
Over the years I have tangentially observed this issue or problem in terms of bankruptcy. I use to represent consumers in filing bankruptcy in a different life. Many people who file bankruptcy are government employees that have a security clearance. Typically, a government employee with money or debt problems can have his or her security clearance jeopardized. If they file bankruptcy, it might not be jeopardized. This is one reason that I use to seek out federal employees who were in need of bankruptcy.
Needless to say, there are a lot of people who have, who want, or who need to obtain or keep their security clearance. Typically, if they lose it, they will find themselves destitute.
In short, a security clearance is about the ability to make a living.
There is also an issue of pride, and a denial or revocation of a security clearance is tantamount to ruining somebody's good name. So, it can tend to be personal.
There are a number of law firms and lawyers that deal with these issues. Among these you will find Tully Rinckey, The Edmonds Law Firm, Berry/Berry PLLC, Sheldon I. Cohen, Cleary & Green LLP, Burnham & Gorokhov PLLC, and many others using Google. You can learn a lot by reading through their websites and blogs.
There are a number of videos on YouTube that apply to this area as well. Below are a few that you might find helpful.
It sounds like niche practice you might need to look into.