The top executive for health insurer Aetna essentially threatened to leave Obamacare if the federal government tried to block its merger with Humana.

In a letter obtained by the Huffington Post, Aetna CEO Mark Bertolini wrote last month to the Justice Department that his company would experience a “negative financial impact” if the DOJ were to try to block the proposed merger, making it difficult to continue selling Obamacare plans.