(CNN) President Donald Trump called on lawmakers to come together to address one of the most frustrating and costly aspects of America's health care system for patients -- surprise medical bills.

Trump has made health care a top political issue, starting with his efforts to dismantle Obamacare , and lately has focused on high drug prices

The President announced on Thursday that he's sending a set of principles to Congress that aims to end patients' responsibility for big charges when they unknowingly are treated by out-of-network doctors or hospitals, often in an emergency situation.

"In emergency care situations, patients should never have to bear the burden of out-of-network costs they didn't agree to pay," Trump said at press conference Thursday, standing with a family that was billed nearly $18,000 for a urine drug test that would have carried an in-network charge of just $101. "No family should be blindsided by outrageous medical bills."

Half of Americans say shielding people from surprise medical bills should be a top priority for Congress, according to an April Kaiser Family Foundation poll . That ranks behind lowering drug costs and protecting those with preexisting conditions, but ahead of major changes to the nation's health care system, such as repealing the Affordable Care Act or implementing a national "Medicare for All" plan.

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