CARACAS, Venezuela — Venezuela’s opposition says it is preparing to deliver tens of millions of dollars in food and medicine to ease devastating shortages and undermine the authoritarian rule of Nicolás Maduro. But some major relief organizations are reluctant to cooperate, fearing the plan could turn humanitarian aid into a political weapon.

On Tuesday, the opposition said it would begin stocking warehouses near the Venezuelan border with supplies donated by the United States, Colombia and Venezuelans abroad. The humanitarian aid — baby formula, nutritional supplements, medicine and hospital supplies — could provide the opposition with a tangible way of weakening Mr. Maduro, who has long relied on food handouts to keep his political base loyal during the country’s long economic collapse.

Getting the aid into Venezuela, past Mr. Maduro’s security forces and into the right hands will be a critical test of the opposition’s ability to rally the nation and establish an interim government. While the United States and more than 30 other nations have recognized the opposition leader, Juan Guaidó, as Venezuela’s rightful leader, he and his supporters still need to show that they can run the country effectively.

“We want to provide tangible early results,” said Miguel Pizarro, the opposition lawmaker in charge of organizing the aid delivery. “We can’t wait for the political transition to start reducing the people’s suffering.”