ATHENS — Charles and Liz Lee and their three children had come to see the sights in Athens for their vacation. But it may not be the Acropolis they will remember as much as something else unexpectedly exhilarating, something they had never seen before: demonstrators carrying Communist flags.

“It’s been a little nerve wracking in Athens,” Heather Lee, 18, who was visiting with her family from Birmingham, Mich., said, describing the demonstrations and the sight of Greeks lined up at A.T.M.s. “But looking back, we can also say that we were in Greece at this time in history.”

For Greece’s all-important tourism industry, however, there is no doubt that this moment of history — a decision over the terms of Greece’s bailout, which will face a referendum on Sunday — could not have arrived at a less auspicious time.

This is the beginning of the high season when, for just a few months, hundreds of thousands of Greeks work almost around the clock trying to make enough money to eat, pay bills and take care of their children during the slower months of the rest of the year.