Does USCIS check previous employments in a different country?

Context:

Before moving to the US I worked at a small company in france on contract with a more well known company. I abruptly ended my contract so I do not have contact wit then. Then I started working in the US and my company is started my Green Card Application. They are now asking for a letter of employment from my previous company. I am not sure how to go about it. Thanks!