Account representatives from Epic Systems, one of the largest providers of medical record systems, have started calling customers with a clear message: We will not be pursuing further integrations with Google Cloud.

Epic's reps told customers the company would instead focus its energies on Amazon Web Services and Microsoft Azure. They said the company decided to halt development with Google Cloud because it wasn't seeing sufficient interest among its health system customers to warrant the investment.

The calls have come in the past few weeks, said three people with knowledge of the matter, and were directed to Epic's hospital customers that use Google's cloud-based technology either for medical research, data storage or for their basic IT operations, including file-sharing. These people declined to be named because they were not authorized to speak for their organizations on the matter.

Privately held Epic is one of the largest electronic medical record companies in the U.S. It sells its products, which include a digital equivalent of the traditional doctor's paper medical chart as well as billing tools, into the largest hospital systems in the U.S. Epic installations are major undertakings, and can end up costing billions of dollars overall. Once installed, they become a core part of a hospital's information systems and are seldom dislodged.

Epic's decision is a blow to Google's efforts to find new customer segments for its cloud products, as the company lags well behind Amazon Web Services and Microsoft Azure in market share for cloud computing. The company is hoping to catch up by landing big-name customers such as Mayo Clinic, and by stressing its artificial intelligence and machine-learning capabilities.

The move comes as Google is facing criticism from privacy advocates about its work with Ascension, one of the largest U.S. health systems. The news broke that a small number of Google employees had access to Ascension patients' protected health information after the two organizations signed a deal to move health information into Google's servers. Google has subsequently said that it is "super proud" of this work with Ascension, and that it hopes to leverage the data for good to develop technologies to detect disease earlier, as well as a tool for doctors and nurses to more easily search their medical record systems, including Epic.

Epic declined to comment on Google or any other vendor specifically but said it considers several factors when deciding which third-party technology providers to support.

"We invest substantial time and engineering effort in evaluating and understanding the infrastructure Epic runs on. Scalability, reliability, and security are important factors we consider when evaluating these underlying technologies," said Epic's vice president of research and development, Seth Hain, in a statement. He said Epic focuses on supporting "infrastructure the Epic community uses today and is likely to use in the future."

A spokesperson for Google Cloud declined to comment on the relationship with Epic.

One of the health system customers who got the call said this could impact their data sharing and aggregation efforts going forward. This person said medical records providers such as Epic and its chief rival, Cerner, are picky with data-sharing standards, and withdrawing support for Google would make it risky for the hospital system to keep using it.

Epic isn't alone in its move.

The Wall Street Journal recently reported that Cerner decided against pursuing a data-storage relationship with Google despite being offered tens of millions of dollars in incentives. The company was on the hunt for a cloud vendor to help it store 250 million patient medical records. In the end, Cerner went with Amazon.

"We've historically seen hospital systems make these decisions independently of their medical record provider," said Aneesh Chopra, the president of health-technology company CareJourney and the former chief technology officer of the United States. "It will be interesting to see if Epic's thumb on the scale moves cloud market share."