Washington (CNN) The leader of a major veterans group is urging President Donald Trump to "reconsider" his appointment of a Defense Department official to serve as the acting secretary of Veterans Affairs amid a brewing controversy over the departure of former VA Secretary David Shulkin last week.

In a letter obtained by CNN and sent to the White House on Tuesday, AMVETS national commander Marion Polk wrote to Trump that "as the VA's second in command, the law predesignates" Deputy VA Secretary Thomas Bowman to serve as acting secretary "as prescribed by federal law."

The push from one of the nation's major veterans groups comes as the White House and Shulkin are in a dispute over whether Shulkin was fired or resigned his job last week. Shulkin has repeatedly said he was fired, while the White House has said he resigned.

The distinction between the two has raised legal questions about whether the President has the authority to install a replacement of his choice for a Cabinet secretary if the official is fired.

The Federal Vacancies Reform Act of 1998 gives the President broad authority to temporarily fill a federal agency vacancy if the person holding the job dies, resigns or is unable to perform the functions and duties of their office. The law, though, does not explicitly say that the President retains that authority if the official is fired.

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