It is peak tourist season in Greece, and on the pristine Monastiri beach on the northern tip of Paros island, a phalanx of lounge chairs with red umbrellas covers the sand. At 70 euros for a pair of front-row seats near the crystalline waters, less than half were taken on a recent day, as Greeks and tourists alike who did not want to pay instead sheltered from the sun under nearby trees.

“In some cases they covered 100 percent of the beach,” said Nicolas Stephanou, 70, a local resident. “We feel we’re being pushed off the island,” he added, explaining that people are made to feel unwelcome unless they use the services of the beach bars that own the chairs.

Many local people like Mr. Stephanou have had enough, saying seaside businesses have left them hardly a scrap of sand on which to lay their towels. In recent weeks, hundreds of people of all ages have staged demonstrations, walking along the sand on three beaches with banners saying “Reclaim our beaches,” as part of a movement called Save Paros Beaches.

Since starting in July, the protests have caught on nationwide, inspiring a “beach towel movement” organized over social media from Corfu in the north to Crete in the south.

While beaches are public in Greece, local authorities lease sections of them to bars, restaurants and hotels. Though no more than 50 percent of a beach is supposed to be occupied, many of the businesses are expanding illegally, occupying more space than they leased.

On Paros, which sees its population of 14,000 increase by tenfold in the summer, those businesses have become predatory, residents say, charging up to 120 euros, or about $130, for “V.I.P.” sun loungers.

Tourists are not too happy about the proliferation of the chairs, either.

On the island’s Kolymbithres beach, 10 rows of lounge chairs recently occupied one sandy cove.

Vasileios Paraskevas, a 47-year-old car factory worker from Germany, said he and his wife couldn’t find room for their own umbrella. “We couldn’t go left, we couldn’t go right,” said Mr. Paraskevas, who ended up sheltering under a tree. “There was no space for us…”