AD watchdogs have received a series of complaints about Ryanair's "offensive" new promotion.
The budget airline faces investigation for using a picture of Winston Churchill to sell its low-cost tickets. The wartime leader is shown in the classic V for victory pose under the tagline: "Let's beat terrorism."
A speech bubble says: "Keep Britain flying."
Underneath, it suggests the best way to see off the terror threat is to buy one of its million £25 seats.
Boss Michael O'Leary spent thousands on full-page ads in every national newspaper this week.
The Advertising Standards Authority is deciding if it should take action.
A spokesman said: "We have received complaints saying the strapline is offensive considering a potential terrorist plot has just happened."
But Ryanair insisted customers backed its campaign, "with people saying 'your message to the extremists is very clear'."