The lure used to get uninsured Americans to sign up for health law coverage was the promise of generous premium subsidies. The promise comes with a catch for almost 3 million people earning three to four times the federal poverty rate: They may have to pay up to 9.5% of their income toward that premium before the government subsidy kicks in. That could take a substantial bite from their budgets — potentially as much as $600 a month for a family of three earning $58,590 to $78,120. As a result, some middle-class families may decide health insurance is beyond their reach and pay a penalty rather than buy coverage.