Minneapolis-based accounting firm CliftonLarsonAllen has abandoned its dual CEO management structure a year after it was created in a merger.

The changes made Gordy Viere CEO while co-CEO Kris McMasters has left the company, ending her tenure as the only female CEO among the top national accounting firms.

“During the past few months the board has reviewed the effectiveness of our CEO structure,” she wrote employees in an e-mail. “Based on that review they have decided to discontinue our co-CEO structure.”

Having one CEO “will increase the pace of integration of our two firms and cause less confusion and uncertainty around our strategic initiatives,” McMasters wrote. “Rather than move to a new position in the firm, I have elected to retire.”

Going Concern, an accounting industry blog, published the e-mails that Viere and McMasters sent to the company’s employees. Ellen Trytek, a CliftonLarsonAllen spokeswoman, confirmed Monday that the e-mails were authentic.

“Kris was an integral part of our early merger discussions and instrumental in bringing our two firms together,” Viere wrote in his e-mail. “Change is never easy, but as hard as these decisions are, they are necessary to build for our firm’s future.”

The co-CEO structure began with the 2012 merger of accounting firms Larson­Allen of Minneapolis, headed by Viere, and Clifton Gunderson of Milwaukee, Wis., headed by McMasters. In 2012, the combined privately owned firm had revenue of $569 million. It has 3,600 employees in 25 states and Washington, D.C.

McMasters also wrote that some of the biggest accomplishments during her tenure were “creating the largest [accounting] firm in the country focused exclusively on private companies and their owners, and being part of an organization that promoted the first and only female CEO of a top 50 accounting firm.”