- Mattis was unhappy that the Trump team decided on businessman Vincent Viola
- Trump's incoming White House press secretary Sean Spicer disputed the account
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.
The source said Mattis was told ahead of the appointment but thought the trading issue should have been raised before the announcement.
Mattis himself wanted Michele Flournoy for a high-level position, according to two people familiar with the matter.
Flournoy was formerly undersecretary for policy under President Barack Obama and was widely believed to be a top contender to be defense secretary had Hillary Clinton won.
Flournoy had preliminary conversations with Mattis and went to New York to brief people on the Trump team on her work on defense and National Security Council reform but withdrew her name from any consideration in mid-December.
Mattis wants a very strong voice in Defense picks and does not want to be limited by the political affiliation of potential nominees, said the same source.
According to another source, who is familiar with the Trump transition, Mattis in the end comes out with a stronger say in choosing whom he wants for the other positions, despite the bumpy start.