BUPYEONG, South Korea — When sales at his clothing shop began sliding several years ago, In Tae-yeon first attributed the drop to a bad economy. But he said he soon realized that the real culprit was something else: hypermarkets crowding into busy commercial districts, attracting shoppers with their easy-to-use parking lots, flashy signs and cutthroat discounts and, as Mr. In put it, “sucking the life out of small-business men like me, like vampires.”

The arrival of hypermarkets — vast department stores that also contain supermarkets — is relatively new in South Korea; a few began opening two decades ago. But they are unique in the country because most are owned by chaebol, the family-controlled conglomerates whose dominance in large and increasingly diverse swaths of the economy is prompting many in South Korea to refer to the country as the Republic of Chaebol.

Rapidly expanding nationwide chains of hypermarkets, supermarkets and 24-hour-a-day convenience stores are the latest and perhaps most visible examples of the penchant among the chaebol for seemingly relentless growth. Total revenue at hypermarkets grew to 33.7 trillion won, or $30.3 billion, in 2010 from 23.7 trillion won in 2005, according to Statistics Korea, the national statistical agency. During the same period, sales at traditional markets, where individual dealers sell products as varied as manufactured goods, meat and farm produce, declined to 24 trillion won from 32.7 trillion won, according to the government’s Agency for Traditional Market Administration.

So when owners of small stores, like Mr. In, began pushing back, picketing hypermarkets and lobbying lawmakers, they started a South Korean version of the “We are the 99 percent” campaign — a movement in support of what is called “economic democratization.”