Used when questioning whether someone has the right or justification to do something, often in negative or interrogative expressions like 筋合いはない (have no right) or そんな筋合いはない (you have no right to do that).
You have no right to say such a thing to me.
I don't think he has any reason to be angry.
Standard spelling with high frequency in news sources.
Variant spelling without the final い; less common than 筋合い.
Compound of 筋 (すじ, 'line, logic, reason') and 合い (あい, 'mutual, together'). The combination conveys a sense of logical coherence or rightful claim.