JQL to show all of user stories under of some Epics with specific label

[Liu Maggie]

I have many Epics with Label "Client-Features", and there are some user stories under these Epics. I want to search all of these user stories, how to write the filter JQL to search them?

[Payne]

You can type 

"Epic Link" = "Client-Features"

in the advanced JQL box; if you press the Enter key, Jira will convert the name of the epic to the issue key (e.g. KEY-12345), but it will work as expected.

EDIT: I re-read your question, and I don't think this will work for you. I missed your point of having several epics with a shared label.