Choosing which tests to run with junit tags

Suppose I have these 3 classes:

@WithTagValuesOf({"endpoint:gateway", "gateway:apps", "tests:a"})
ClassX {}
@WithTagValuesOf({"endpoint:gateway", "gateway:apps", "tests:b"})
ClassY {}
@WithTagValuesOf({"endpoint:gateway", "gateway:portals", "tests:b"})
ClassZ {}

If I want to only run ClassY tests which flags should I use? I'm using mvn verify -Dtags="gateway:apps,tests:b" and it runs all tests with gateway:apps tag.