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.

Trump tweeted last week that Robert Wilkie, a Defense Department official, would serve as acting secretary.

The President has nominated White House physician Ronny Jackson to permanently lead the department. He awaits confirmation in the Senate.

Most veterans groups have not weighed in on Trump’s decision to bring Wilkie into VA from the Defense Department, though they were largely supportive of Shulkin and had implored the White House to keep him in the role. Many have expressed concerns publicly about Trump’s selection of Jackson to lead VA, the federal government’s second largest agency, saying that Jackson may not have adequate management experience.

While Wilkie “may be a very bright person and leader, he does not know the VA or its problems,” Polk wrote. “He’s at square one, as any outsider would be. And while there’s no doubt he would grow into the position over time, veterans don’t have that time.”

Polk also said that Bowman is an “exceedingly qualified and experienced public servant intimately familiar with the VA and currently holding the position federal law designates to become acting secretary.”

“Sidestepping Bowman in favor of an outsider wholly unfamiliar with the VA is a confusing choice that only serves to erode confidence in the VA as an institution during this critical time,” Polk added.

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