BRATISLAVA, Slovakia — In a television advertisement for the popular Slovak beer Zlaty Bazant, a grinning man with a paunch stands on a sunny beach, nodding his head as the narrator says, “To want to borrow from everyone, that is Greek.” The ad then cuts to a skinny man, standing in a field, who shakes his head. “To not want to lend to anyone,” the narrator says, “that is Slovak.”

The commercial has touched a nerve here in the second-poorest country in the euro currency zone, where the average worker earns just over $1,000 a month. The prospect of guaranteeing the debt of richer but more spendthrift countries like Greece, Portugal and even Italy has led to public outrage. So much so that tiny Slovakia now threatens to derail a collective European bailout fund to shore up the euro, which requires the approval of all 17 countries that use the currency.

Once among the most enthusiastic new members of the European Union, and an early adopter of the euro in Eastern Europe, Slovakia is proud of its strong growth and eager to leave behind its reputation as the “other half” of Czechoslovakia. But it has also become a stark example of the love-hate relationship that many residents of the Continent have begun to feel toward a united Europe.

Adopting the euro required hard sacrifices here that stand in sharp contrast to reports of overspending and mismanagement in Greece. The worries about the union’s future are all too real in smaller, poorer countries like Slovakia, which has about 5.5 million people, and is being asked to contribute $10 billion in debt guarantees to a $590 billion euro zone stability fund.