A federal government mandate went into effect this year requiring hospitals to publish prices for imaging and other healthcare services they negotiate with private insurers. But a new investigation reveals why so many trade groups and hospital associations have fought to block the requirement.

Hospitals are charging patients vastly different amounts for the same services, including X-rays, MRI scans, colonoscopies, pregnancy tests and more. The New York Times partnered with two University of Maryland-Baltimore County researchers to review medical costs at 60 major hospitals, releasing their bombshell report on Aug. 22.

In terms of imaging, a patient with UnitedHealthcare’s HMO plan should expect to pay $1,093 for an MRI at Aurora St. Luke’s in Milwaukee. With the same private insurer’s PPO plan, however, the exam runs for more than $4,000.

At Mass General in Boston, a knee MRI costs anywhere from $830-$4,000 depending on an individual’s insurance plan. And if you want to pay in cash, bring around $3,105 for the exam, the Times reported.

The five largest insurers all declined on-the-record interviews. And Vice President for public policy at the American Hospital Association says "these rate sheets are not helpful to anyone,” adding “... a lot of hospitals are putting in a lot of effort to comply with the rule.”

Six months after these rules went into effect, the Times found the 10 highest-revenue hospitals had posted little to no data on their websites.

The Centers for Medicare & Medicaid Services has said those dodging pricing transparency rules could face fines of up to $2 million.

“It’s not just individual patients who are in the dark,” Martin Gaynor, a Carnegie Mellon economist who studies health pricing, told the news outlet. “Employers are in the dark. Governments are in the dark. It’s just astonishing how deeply ignorant we are about these prices.”

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