Venezuelan opposition leader Henrique Capriles has said that more than 70,000 people who endorsed a petition for a referendum to oust President Nicolas Maduro had their signatures validated on Monday.
Just under 200,000 valid signatures are needed for the process to go ahead.
Mr Maduro was elected in April 2013 and his term runs until 2019.
The opposition blames his socialist policies for rampant inflation and the shortage of food and basic goods.
Mr Capriles said the massive presence of voters on the first day of the validation process was a clear sign that Venezuelans wanted a change of government.
"What we saw today were queues across the country," said Mr Capriles. "That's a warning for Maduro."
Those who endorsed the petition will have until Friday to have their identity cards and fingerprints checked in posts set up by the National Electoral Council (CNE).
The petition had almost two million signatures but election officials said 600,000 of those were fraudulent.
Only 1% of the electorate, or 194,729 voters, however, need to endorse the referendum in this first phase.
According to Mr Capriles, quoting official CNE figures, 71,557 signatures were authenticated on Monday.
The opposition says that under Mr Maduro's socialist government and that of his predecessor in office, the late Hugo Chavez, the oil-rich country was mismanaged to the point of collapse.
The government says the country's problems, which include the world's highest inflation and shortages of basic goods, are due to an economic war being waged by "imperialist forces".
Timing is key
Opposition leaders handed in the petition on 2 May calling for a recall referendum.
They want the vote to be held this year, as its timing is key for what happens next.
Should the referendum be held before 10 January and go against Mr Maduro, fresh elections will be triggered.
But if the vote were to be held after 10 January - in the last two years of Mr Maduro's mandate - he would be replaced by his vice-president and supporter, Aristobulo Isturiz.
The opposition still has to overcome a number of hurdles before a recall referendum can be held.
If enough signatures on this initial petition are validated, opposition leaders will have to hand in a second petition signed by almost four million people.
Only when the electoral authorities have established that the requirements have been met on that second petition will the recall referendum be held.
Steps towards the recall referendum
- 1% of voters on the electoral roll have to sign a petition within 30 days to kick-start the process
- Signatures have to be validated
- 20% of voters (almost four million) have to sign a second petition in order to trigger the referendum
- For the referendum to be successful, an equal or greater number of voters than those who elected Mr Maduro would have to cast their vote in favour of the recall - he won the 2013 election with 7,587,579 votes