The pickets are part of a protest begun 2006 after Uruguay launched a eucalyptus pulp mill the campaigners say damages the ecology of the Uruguay river and surrounding area.
Argentina went to the International Court of Justice in The Hague in support of the environmentalist concerns but its claim was thrown out. Although Uruguay was reprimanded for failing to consult with Argentina over the mill operations, the court ruling April 20 signaled the end of the line for the anti-mill protest. The judges said they saw no evidence the river was polluted by the pulp mill.
Unfazed pickets refused to budge, however, maintaining the area's ecology was at risk from the Finnish-built pulping complex. Scientific reports accepted by the world court in support of Uruguay's contention that the mill posed no ecological risk also went unheeded by the protesters, who are aligned with environmental groups in Argentina and elsewhere.
The campaign groups say the court ruling was a victory for business over public interests.
The pickets were originally endorsed by Argentine President Cristina Fernandez de Kirchner but after the ruling Buenos Aires began moving away from that position in a bid to normalize ties with Uruguay's popular new President Jose Mujica and capitalize on business opportunities.
So far, Fernandez has been thwarted by the protesters. After the latest round of summit talks this week between Fernandez and Mujica, officials said the two sides now would seek legal redress from the courts.
Analysts said the government could be headed for a long legal battle unless it negotiated with the pickets with the aim of striking a compromise, as the protesters seem in no mood to surrender unconditionally.
The Gualeguaychu-Fray Bentos bridge, crucial to increasing bilateral trade, has been practically inaccessible for that purpose since the row began in 2006. Citizens of the two countries wanting to visit friends and families use ferries across the river in a long and expensive process.
The latest talks made progress elsewhere on the pulp mill issues. Fernandez and Mujica agreed to work on a timetable to jointly monitor the quality of the river water and watch for any effect of the pulp mill operations on the river and its surroundings.
In a major reversal of her position, Fernandez said, "Pickets are not illegal but illegitimate."
She added, "Some pickets are rational, others are violent. It's a methodology I disagree with, but it's up to the courts to decide."
Argentine Foreign Minister Jorge Taiana issued an assurance that "justice can have a role" in solving the conflict -- a hint the government would be seeking some compromise, though it wasn't clear what that could be.
Before Mujica took the initiative to seek a resolution of the dispute, soon after his inauguration in March, Argentina's government backed the pickets -- a policy that now has come to haunt Fernandez.
Efforts toward normalization have gained support also because of former guerrilla leader Mujica's standing across a wide political spectrum.
Argentine officials told the media the government was now keen on resolving issues with Uruguay.