The U.S. Treasury Department levied sanctions on Mexican trading company Libre Abordo SA de CV for buying Venezuelan oil via oil-for-humanitarian-aid agreements with the embattled country.

Libre Abordo and its affiliate Schlager Business Group purchased 32 million barrels of crude oil this year to become the biggest supporter of Venezuela’s struggling oil industry under the regime of President Nicolas Maduro.

Company shareholders 23-year-old Olga Maria Zepeda Esparza and Veronica Esparza Garcia were also added to the list, along with Joaquin Leal Jimenez Garcia, according to a notice from the Treasury Department’s Office of Foreign Asset Control. Jimenez was an oil trader for Libre Abordo, according to documents seen by Bloomberg.

The U.S. also beefed up sanctions against shipping companies Delos Voyager Shipping Ltd and Romina Maritime Co and the vessels Delos Voyager and Euroforce for transporting oil produced by state-owned Petroleos de Venezuela SA. Other companies included in the list are Washington Trading Ltd, partly owned by Zepeda Esparza, Luzy Technologies, Cosmo Resources Pte Ltd and Alel Technologies.

Libre signed a contract with Venezuela’s ’s state foreign trade corporation, known as Corpovex, to export water tank trucks and corn in exchange for crude oil. The contracts were worth 195.5 million euros ($217 million) but over the course of its execution Libre and Schlager received oil worth more than $300 million, according to documents seen by Bloomberg.

Libre Abordo agreed to lift and sell oil in a scheme orchestrated by Leal Jimenez and Alex Nain Saab Moran, a Colombian businessman seen by U.S. authorities as a dealmaker for Maduro, according to the Treasury.

The Trump administration has been targeting Venezuela’s oil trade as the commodity accounts for 95% of the inflow of foreign currency into the country. Exports of crude oil fell to 322,183 barrels daily in May to levels not seen since 1947, according to shipping reports and ship-tracking data compiled by Bloomberg.