CARACAS, Venezuela—President Nicolás Maduro’s administration seized three dozen stores in a supermarket chain and accused the company of hoarding goods in a plot to destabilize the government, stepping up a crackdown on the private sector amid a collapsing economy.

Mr. Maduro has blamed soaring inflation and shortages of basic goods on a conspiracy he calls an “economic war.” His approval rating has fallen rapidly and he now has the support of one in five Venezuelans.

...