'strike-proof' is a modern compound formed from the noun 'strike' (as in a work stoppage) and the suffix 'proof' meaning 'resistant to' or 'impervious to'.

'strike' (work stoppage) developed as a sense of the verb 'strike' and became common in the 19th century in industrial contexts; the adjective-forming use of '-proof' (as in 'waterproof', 'bulletproof') has been productive since the 16th–19th centuries, and compounds like 'strike-proof' arose by analogy in modern industrial/labor vocabulary.

Originally the parts meant 'to strike' and 'able to be tested' (from 'proof' in the sense of 'tested' or 'resistant'); combined in modern English they specifically mean 'resistant to strikes' rather than their separate literal senses.