Melania Trump did 10 modelling jobs in the US in the seven weeks before she was legally allowed to work in the country, earning her $20,056, according to reports.
The news of Melania Trump's breach of immigration law comes days before the US election takes place. In the race for the White House, her husband Donald Trump has been taking a hard line on immigration laws and those who break them.
The Republican nominee has said there should be wider use of the government's E-verify system to enable employers to check whether or not people are allowed to work.
Melania Trump secured a green card in March 2001, and became a US citizen in 2006. She has always claimed that she has never broken the US' immigration laws, and has used this as a way to argue for her husband's stance on immigration.
She took on the 10 jobs between 10 September and 15 October, a period during which she was allowed do search for work, but was not permitted to do any paid work, according to documents seen by the Associated Press.
In a speech on Thursday - her first on the campaign trail for months - she said: "As a young entrepreneur, I wanted to follow my dream to a place where freedom and opportunity were in abundance. So of course, I came here.
"Living and working in America was a true blessing, but I wanted something more. I wanted to be an American."