What they did was not ethecal.
Unfortunately it is what happens in the controls industry and many other similar industries, almost every day.
Your situation may have a couple of issues that would likely cause your legal council to advise you to be more careful in the future, but that you do not have gounds for a successful "cause of action":
1. Unless you can factually prove that you lost money directly caused by them using you drawings, you will not likely sustain a cause of action. Even if you did win, the only results would likely be your lost profit on that project, likely not enough to cover the cost of litigation.
2. There is very little "original concept" in any control engineering drawings in the last 10 to 20 years. Chances are that some portion of your "engineering drawings", could be derivative work of others that you may have over time, customized onto your title block, this however doesn't make your work "original work". I am not saying that that is what you did, but they would test you "originality" in the discovery process.
3. We have used non disclosure and non compete contracts to prevent this, and I still find my original works on plubic plans and specs by large engineering firms (cut and paste functionality is the first thing designers seem to learn in school).
Anyway, sorry to see you experience this, yet, learn from it, and now you will be a bit smarter as time moves on.
Best part of it, you discovered a RAT that you should nave no further dealings with.
Good luck
Drac
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