Venezuela’s opposition-controlled National Assembly is questioning the legality of a $500 million deal Rosneft OJSC made with the state oil company to increase its stake in a local oil venture. The congressional oil commission agreed on Wednesday to reject any oil deal signed by the executive branch without approval from the National Assembly, according to a copy of the declaration provided to Bloomberg News by Milagros Paz, an opposition deputy. Their proposal must now go to the National Assembly for approval. President Nicolas Maduro announced on Feb. 20 that Rosneft would pay cash-strapped Petroleos de Venezuela SA $500 million to increase ownership in the Petromonagas crude-processing joint venture to 40 percent from 16.7 percent. A battle over the deal could deepen an institutional standoff between Congress and Maduro as they spar over economic and political policy. The Supreme Court has denied previous congressional attempts to block Maduro’s executive powers. “The deal is illegal because the government overstepped the National Assembly,” Paz said in an interview in Caracas. The declaration cites Article 150 of the constitution that says contracts of national interest can’t be signed without approval from the National Assembly.