The US ambassador to Canada announced his resignation Friday, becoming the first to yield to a demand by Donald Trump that politically appointed ambassadors quit by Inauguration Day.

"As requested I have resigned as US Ambassador to Canada effective 1/20," Bruce Heyman wrote on Twitter. Heyman is close to outgoing President Barack Obama.

The New York Times reported Thursday that the Trump transition team has issued a blanket order requiring politically appointed ambassadors — as opposed to career diplomats holding such posts — to leave their overseas positions by Inauguration Day on Jan. 20. The paper quoted ambassadors familiar with the plan.

Political appointees are often close to the president who gave them the job. In the past, they were often allowed to stay in their posts for weeks or months after the president's term ends, the Times said. Trump's move breaks with this precedent.

Heyman, on the job in Ottawa since April 2014, used to work at Goldman Sachs and was a major contributor to Obama's 2008 and 2012 campaigns.

Trump's decision means the United States could be left without ambassadors in important countries for months. The posts require Senate confirmation.