Milinkevich was picked as the unified opposition's presidential candidate at a similar congress in October 2005. Some 800 delegates from all over Belarus were involved in the ballot that gave Milinkevich a narrow edge over United Civic Party leader Anatol Lyabedzka.
Following the March 19, 2006 presidential election -- in which he officially obtained 6 percent of the vote -- Milinkevich became the primary voice of the Belarusian opposition in the West.
Milinkevich has been regularly received by high-ranking European politicians. In October 2006, he was honored with the European Parliament's prestigious Sakharov Prize for freedom of thought.
Milinkevich's high exposure in the West may have aroused envy among fellow opposition leaders like Lyabedzka or Belarusian Party of Communists head Syarhey Kalyakin, who also unsuccessfully competed with him for the role of the unified opposition's presidential candidate.
In January of this year, the Political Council of Pro-Democratic Forces -- the coordinating body of the unified opposition, which is formally chaired by Milinkevich -- proposed that the chairmanship become a rotating post open to all party leaders.
This rotational principle is expected to be approved during the March congress. Milinkevich, however, vigorously contested the idea.
"I am not afraid of competition, and am ready to enter the struggle for leadership [of the opposition] once again," he told RFE/RL's Belarus Service. "But when the coalition decided that there would be a rotation, I immediately said that I'm not interested. Because rotation means that there is no leader, and that all are leaders, at the same time. Everyone becomes a leader for a few months and is subsequently replaced. You can be a leader once every three years. [But] you cannot beat the dictatorship with such an unclenched fist."
Milinkevich also suggested that the procedure for selecting delegates to attend the congress was far from transparent, and subject to "manipulation" by other aspirants to the role of unified opposition head.
Independent trade unionist Alyaksandr Bukhvostau, the organizer of the March congress, said Milinkevich's refusal to participate represented a "split" in the opposition ranks.
Communist Party head Kalyakin -- who managed Milinkevich's election headquarters in the run-up to the 2006 presidential vote -- has accused Milinkevich of skipping the congress out of fear of losing the leadership post.
"In my opinion, the man is simply not sure he can get support at this congress," Kalyakin said. "Therefore, he's given up without even trying to compete in this matter. Anyone giving up is not right."
"A congress without Milinkevich cannot be a congress of united democratic forces. But Milinkevich without the united democratic forces is not a nationwide leader either."
Lyabedzka, who clearly has leadership ambitions of his own, sees Milinkevich's refusal to participate in the opposition congress as his formal withdrawal from politics.
"It is apparent that from this moment on, the united democratic forces have neither a de jure nor a de facto leader," Lyabedzka told RFE/RL. "Milinkevich has probably decided to return to the place from which he entered politics -- the civic sector."
But not everyone in the opposition seems certain that Milinkevich's departure is the best way to resolve the leadership controversy. One such politician is Vintsuk Vyachorka, head of the Belarusian Popular Front Party, which strongly backed Milinkevich as the single presidential challenger during the 2005 opposition congress.
Vyachorka believes the widening animosity between Milinkevich and the remainder of the Political Council of Pro-Democratic Forces may end up harming both sides.
"We understand that a congress without Milinkevich cannot be a congress of united democratic forces," Vyachorka said. "But Milinkevich without the united democratic forces is not a nationwide leader either."
To avoid such a situation, Vyachorka has proposed a compromise "for the sake of unity," whereby Milinkevich would remain chairman of the
Political Council of Pro-Democratic Forces and continue to serve as the
opposition's key representative in the West. This position could be confirmed by the opposition congress, which Vyachorka has proposed be postponed until May.
At the same time, Vyachorka has suggested the creation of a post of chairman of a presidium to the Political Council of Pro-Democratic Forces, which could be held by other party leaders on a rotational basis. According to Vyachorka, the presidium chairman could keep an eye on the council chairman, and vice versa.
It remains to be seen whether Vyachorka's proposal is viable. The council held a meeting on February 19 to discuss the idea, but ended without a conclusive decision.
The controversy comes at a time when the Belarusian opposition could be playing an important role in shaping the country's future.
Belarus's energy-price row with Russia has prompted Lukashenka to make rare overtures toward the West. A confident opposition -- one that was able to speak with one voice both at home and abroad -- could help forge those ties.
As it stands, however, the opposition is weak and unable to significantly influence the political situation. If the rift over its leadership continues to fester, the opposition may fail at a time that could otherwise prove its greatest political hour.
Click on the image to view a photo gallery of election-day events in Belarus.
THE BELARUS ELECTION: To view a complete archive of RFE/RL's coverage of the March 19 presidential election, click here.
To read and listen to RFE/RL's Belarus Service's coverage of the vote in Belarusian, click here.