1
general::
Also, muscle in on. Forcibly intrude on or interfere with something, as in The children were determined not to allow the school bully to muscle in, or No more muscling in on our policy decisions! [Colloquial; 1920s]
American Heritage Idioms
2
general::
Phrase(s): muscle in (on someone or something)
to try forcefully to displace someone or take over someone’s property, interests, or relationships. • Are you trying to muscle in on my scheme? • If you try to muscle in, you’ll be facing big trouble.
McGrawhill's American Idioms And Phrasal Verbs