Story highlights Mattis was unhappy that the Trump team decided on businessman Vincent Viola

Trump's incoming White House press secretary Sean Spicer disputed the account

Washington (CNN) The Trump transition team clashed with former Gen. James Mattis, the President-elect's choice for secretary of defense, over the transition selecting a secretary of the Army without his input, several sources told CNN.

Mattis was angry and threatened to quit if the transition tried to appoint more people without him, one of the sources said. Vice President-elect Mike Pence had to talk to Mattis and smooth things over, the source added.

The Washington Post first reported the disagreement.

Trump's incoming White House press secretary Sean Spicer disputed the story in a Tweet Friday morning, writing, "Great transition at DoD. Reports to contrary completely false and come from sources who do not have any knowledge of our transition efforts."

Mattis was unhappy that the team decided on businessman Vincent Viola without consulting him. He also expressed concern after learning of questionable stock trading practices in Viola's trading firm, one source said.

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