1
general::
Criticized or held responsible, as in The landlord is under fire for not repairing the roof. This expression originally referred to being within range of enemy guns; its figurative use dates from the late 1800s.
American Heritage Idioms
2
general::
Phrase(s): *under fire
Fig. during an attack; being attacked. (*Typically: be ~; resign ~; think ~.) • There was a scandal in city hall, and the mayor was forced to resign under fire. • John is a good lawyer because he can think under fire.
McGrawhill's American Idioms And Phrasal Verbs