Comments by Epic's head of interoperability in a Senate HELP Committee Tuesday have triggered members of the CommonWell Health Alliance, the subject of some of the comments, to fire back at the Verona, Wisconsin-based EHR giant. 

Peter DeVault, Epic's director of interoperability, spoke before the Senate committee on the topic of interoperability and Epic's role in moving it forward. In the questions portion of the hearing, Senator Tammy Baldwin, D-Wisconsin, shifted the conversation, asking DeVault candidly: Why isn't Epic a part of CommonWell?

[See also: Interoperability (finally) takes center stage in Congress.]

Short answer? They're not too keen on the hefty price tag of joining, not to mention the non-disclosure agreement that would be required.

"When we were approached by them and asked to join, we were told that it would be multiple millions of dollars for us to join and that we would have to sign an NDA," said DeVault. "To us, the only reasons to have an NDA are if they're going to tell you something that otherwise they wouldn't want people to know" - which he said could include the possibility they may sell data downstream or wanted to ensure there were no intellectual property conflicts.

"That lack of transparency didn't sit well with us," he said.

CommonWell, a vendor-led interoperability effort whose members include competitors such as Cerner, McKesson, athenahealth and Greenway, fired back, with a representative contacting Healthcare IT News with a response to DeVault's comments.

"We are committed to openness and transparency," the statement read. "Accordingly we publish our services and use case specifications, along with our nominal membership and service fees on our website for everyone to see."

According to CommonWell's membership and service fee structure, a company of Epic's revenue size – $1.8 billion in 2014 – would indeed pay in the millions, $1.25 million, in fact, for an annual subscription fee and an additional $50,000 to $90,000 in annual membership dues were it to join. 

On Wednesday night, athenahealth CEO Jonathan Bush got even more personal on Twitter, going after Epic CEO Judy Faulkner directly regarding the price. 

Judy, Judy, Judy. Can't afford 1.4M? Puh-leese! @athenahealth will for you. Join @CommonWell and lets connect.

— Jonathan Bush (@Jonathan_Bush) March 18, 2015

At the senate hearing, DeVault also underscored CommonWell's low participant numbers in its interoperability project so far – which he called an "aspiring network," noting a stark difference when compared to Epic's Care Everywhere network.

The two-year old CommonWell has 1,000 physicians live on it, he said, compared to 100,000 physicians on Epic's Care Everywhere. Healthcare IT News reached out to CommonWell officials for the most up-to-date number but did not receive a response by publication time. 

DeVault's comments didn't sit well with one of CommonWell's founding members (and one of Epic's chief competitors), Cerner. 

His "rhetoric is a slap in the face to many parties working to advance interoperability," according to a statement released by Cerner officials shortly after the committee hearing. "It was discouraging to hear more potshots and false statements when it's clear there is real work to be done. We're committed to CommonWell as a practical, market-led way to achieve meaningful interoperability."

There's been tension between Epic and CommonWell ever since the latter group's launch at the 2013 HIMSS Annual Conference & Exhibition.

At that HIMSS13 announcement, athenahealth CEO Jonathan Bush emphasized that anyone was invited to CommonWell – even a vendor of "epic proportions."

In a subsequent interview, Healthcare IT News asked McKesson CEO John Hammergren whether that invitation was dangled only because the founding companies suspected Epic wouldn't bite.

"We'd like them to bite! We want them to bite," said Hammergren. "I'm hopeful that they will see it the same way we see it."

[See also: Q&A: McKesson and Cerner execs discuss CommonWell Health Alliance.]

But Epic CEO Judy Faulkner noted that her company wasn't asked to join before the announcement. "We did not know about it. We were not invited," Faulkner told Bloomberg back in 2013. "It appears on the surface to be used as a competitive weapon, and that's just wrong. It's wrong for the country."