On Sunday, Costa Ricans will go to the polls to decide whether or not to participate in the Central American Free Trade Agreement. Despite being one of the countries most open to trade in Latin America, Costa Rica is the only signatory nation that has not yet ratified this agreement, and it may become the only one to reject it. But if the country continues on the course it’s on, Costa Ricans may also reject an essential foundation of its liberal democracy: the peaceful resolution of internal debates.

For over four years, Costa Ricans have been discussing the merits of CAFTA. The debate intensified in April of this year when president Oscar Arias called a referendum—the first in the country’s history—to break the deadlock over the issue in Congress, where a minority of legislators was filibustering approval of the agreement. Back then, polls showed a thirty-point lead for CAFTA supporters. Now, a poll released Thursday shows CAFTA trailing by 12 points.

CAFTA’s opponents have routinely threatened its supporters with violence, and supporters have often had to be escorted by police during community debates. In public universities, students who favor the agreement have been physically prevented from distributing literature, and in one widely publicized case, a student was attacked.

The leader of the NO campaign, Eugenio Trejos, president of the state-owned Technological Institute, has repeatedly claimed that CAFTA will pass over his dead body.

These events are especially disturbing coming from a country that is considered one of the most stable democracies on the continent. The CAFTA debate reveals the extent to which the radical left is willing to undermine even the democratic institutions that have long set Costa Rica apart from most of Latin America.

Since the beginning of the campaign, the “NO to CAFTA” camp—constituted mostly by public-university faculties, college students, public unions, and intellectuals—have cast doubts about the independence of the Electoral Tribunal. Their strategy was quite obviously based on refusing to recognize an eventual defeat in the polls. CAFTA’s opponents intensified their assault after the Constitutional Court ruled last July that the agreement did not violate the Constitution. This led to claims that the Electoral Tribunal and the Constitutional Court, along with the “corporate media,” were all in the pockets of the Arias administration and big businesses.

The NO camp has repeatedly claimed that the basic conditions for a “fair” vote—e.g., equal access to media advertisement—have not been met, thus enabling them to disregard a defeat under democratic processes. CAFTA’s opponents talk of beating the treaty through “democracy of the streets,” which means massive blockades of roads and ports that will bring the country to a halt.

Unfortunately, the prospects of approving CAFTA have been compromised even further by the leak last month of a private memorandum from Vice President Kevin Casas to President Arias, in which Casas suggested, among other things, withholding public money to mayors who failed to deliver their districts’ votes on CAFTA, and circumventing some electoral rules. The ensuing scandal led to Casas’ resignation and caused a dramatic fall in CAFTA’s popularity. In a matter of two weeks, the YES camp went from having a 20-point lead over the NO to a technical tie. Today, the approval of CAFTA is no longer certain.

The consequences of rejecting CAFTA go beyond the resulting loss of competitiveness to the Costa Rican economy. It would make Oscar Arias a lame duck president only a year and a half into his four-year term, and embolden the hard left leading to the general elections of 2010. It comes as no surprise, then, that Fidel Castro, Hugo Chavez and Daniel Ortega have all publicly called for CAFTA’s defeat in the referendum.

But Costa Ricans are not only deciding on CAFTA next Sunday. They’re deciding also on the future of their liberal democracy and the ways in which they resolve their political disagreements. Hopefully a majority will contemplate those troubling signs when casting their votes.