President Nicolas Maduro warned airlines on Friday not to cut services for Venezuela over billions of dollars they are owed and threatened them with permanent expulsion. Airlines that serve Venezuela are battling to recover $3.7 billion blocked by the government, the head of industry body IATA said this week, accusing Caracas of breaking international rules. Latin American airline Avianca-Taca said Wednesday it was suspending flights between San Jose and Caracas beginning April 7 due to a lack of profitability. Other foreign airlines including Ecuador's Tame, Air Canada, Portugal's TAP and Panama's Copa Airlines have already reduced operations in Venezuela. For an "airline that reduces (operations) I will take severe measures. The company that leaves the country will not return while we hold power," Maduro told a press conference in Caracas. Maduro, the handpicked leftist successor of the late firebrand Hugo Chavez, said that a reduction in operations "was part of the war they want to wage in Venezuela." Venezuelan law requires air tickets to be sold in non-convertible bolivars, the national currency, which the government then exchanges with the airlines using US dollars. But Venezuelan authorities ceased the dollar payments to the airlines in October, the International Air Transport Association (IATA) said. Tony Tyler, who heads IATA, said Wednesday: "Airlines certainly cannot sustain operations indefinitely if they can't get paid."