Fed up with a collapsing economy, Venezuelans have been turning out in huge numbers this week to support a referendum that could potentially end the rule of President Nicolas Maduro and his Socialist Party.

The opposition has to collect hundreds of thousands of signatures as the first step in a complicated process leading to a recall vote on ousting Maduro. The electoral authority gave the opposition five days to verify the signatures. The deadline is Friday, and it's a race against time for both the opposition and the president.

If the opposition gathers enough validated signatures by the end of the week, then the referendum could be held this year. If the opposition wins the recall vote, it means Maduro would be forced out and there would be new elections. The opposition won two-thirds of the parliamentary seats in elections last December and would be favored to win new elections amid chronic shortages of food, medicine, electricity and many other basic goods.

Maduro and his Socialist Party want to prevent a referendum, or at least delay it. He was elected in 2013, and by next year will be in the final two years of his term. Under the constitution, he would still have to step down if he lost a recall vote next year. But because Maduro would be in the latter part of his term, his vice president, Jorge Arreaza, would take over, and the Socialists would remain in power.

The lines at the so-called validation points, where the signatures are being checked, have been longer than the ones at the depleted supermarkets, according to reports. The rhetoric has been vitriolic with each side accusing the other of trying to derail democracy.

"The recall referendum is a constitutional right," says Phillip Gunson from the International Crisis Group in Caracas. "The problem is the government is doing everything fair and foul to block the process. The consequence of course is that by shutting off the safety valve, the pressures will increase. There is a very real danger of violence."

International human rights groups have already said there is a concerted campaign of political repression underway.

"The electoral authority, which is fully controlled by the government, has been deliberately delaying the process, questioning the signatures of Venezuelans who have signed in favor of holding the referendum, " said Jose Miguel Vivanco, from Human Rights Watch. "Venezuela is facing probably the most serious political economic and social crisis in many, many years."

The detention this past Sunday of two opposition political activists has heightened tensions.

Francisco Marquez-Lara and Gabriel San Miguel were working to help people get to the signature validation centers when they were detained, according to their families and supporters.

They were carrying the equivalent of $3,000 and pamphlets supporting the recall, according to reports. The government is accusing them of terrorism, money laundering and attempting to destabilize the country. The opposition says the money was to pay for transportation and food for those traveling long distances to get to the few signature validation centers.

Marquez-Lara is a dual Venezuelan-U.S. citizen and a Harvard graduate. His brother Andres Marquez-Lara, who is in the U.S., spoke to NPR.

"This is another example of political persecution," Andres Marquez-Lara said. "This is an example of the government trying to sabotage a democratic process. That it can't say outright, 'Hey, we are not going to have the referendum,' because then their democratic façade would fall off."

"Franscisco and Gabriel were on their way to support the democratic process," he added. "[They] are two young people who are passionate about Venezuela. Both have dual-nationalities ... and they could go and live somewhere else but they both decided to stay in Venezuela to fight for democracy."

Meanwhile, international pressure is growing. The Organization of American States was holding an emergency meeting Thursday to discuss "the serious abuses of democracy in Venezuela." A senior U.S. diplomat, Thomas Shannon, traveled to Caracas to meet Maduro on Wednesday.

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