President Obama took aim at the health insurance industry Sunday, using an op-ed to accuse the insurance companies of discriminating against millions and rally support for a comprehensive reform package to hold them "accountable."

The op-ed in The New York Times escalated an approach the White House and congressional Democrats have taken in recent weeks, in which they've focused more on Americans who have insurance, rather than the staggering number of uninsured. In doing so, health care reform proponents have cited a litany of examples of how Americans’ health insurance plans are falling short.

Though health care reform critics have flooded town halls over the past month, Obama wrote in his column that media have focused too much on the "loudest voices" — he suggested that those with inadequate insurance policies are clamoring for reform.

"What we haven't heard are the voices of the millions upon millions of Americans who quietly struggle every day with a system that often works better for the health-insurance companies than it does for them," Obama wrote.

The president cited a "2007 national survey" which he said showed insurance companies "discriminated" against more than 12 million Americans over three years because of pre-existing conditions.

"Almost everyone knows that we must start holding insurance companies accountable and give Americans a greater sense of stability and security when it comes to their health care," he wrote.

Obama wrote that he's confident health care reform will pass.

Click here to read Obama's op-ed in The New York Times.