Retired U.S. Marine Gen. James Mattis will step down from his board position at General Dynamics Corp. and give up unvested equity awards if confirmed as President-elect Donald Trump's defense secretary, according to a letter submitted to the Defense Department's ethics lawyer.

In a letter dated Jan. 5 and made public Saturday, Mattis said he would resign from the board and temporarily recuse himself from matters related to the company, the fifth-biggest U.S. defense supplier with $10 billion in contracts last year.

"For a period of one year after my resignation, I will not participate personally and substantially in any particular matter involving specific parties in which I know General Dynamics is a party or represents a party," unless he is authorized to participate, Mattis said. Federal regulations allow for such authorization when it's determined that the government's interest in an official's participation outweighs any reasonable concern related to ethics questions.