“Today, we are struggling for the future of the country and we will not rest,” said Tomás Guanipa, a congressman and leader of the opposition party Primero Justicia. “We will defeat all of the obstacles the government and electoral commission put in our way.”

Mr. Maduro has characterized the effort as a coup attempt. “They go around saying ‘Our hour has come,’” he said of his opponents on television Tuesday night. “Your hour will never come.”

To hold a recall vote, opposition activists must first collect the signatures of one percent of eligible voters. In a second stage, 20 percent of voters would have to agree to the recall for it to be held. Mr. Maduro’s opponents would then have to win the recall with more votes than he received in his initial election, just under 51 percent.

Were Mr. Maduro to be removed this year, elections for a new president would be called.

A coalition of opposition parties defeated Mr. Maduro’s National Socialist Party in elections last December. But Mr. Maduro continues to control most of the levers of power.

That the commission gave the opposition access to the paperwork at all came as a surprise to many in Venezuela. Opposition leaders said that on previous attempts they had been ignored by the commission. One encounter turned violent.