Anibal Romero, an immigration lawyer who has represented a number of former Trump workers and is advising one of those fired from Trump Winery this week, said the pool of undocumented laborers at Trump properties has always been an open secret.

“He’s benefited from undocumented labor for a very long time,” Mr. Romero said.

A year ago, a New York Times story featured undocumented workers who served at Mr. Trump’s properties and had interactions with Mr. Trump himself. That article has since led to others from The Times, Univision and The Washington Post, which first reported on Tuesday the latest round of firings at Trump Winery.

Mr. Romero said he believed the Trump Organization thought it could get away with continuing to hire undocumented laborers, who feared repercussions that could disrupt their lives or livelihoods even though some had worked at Trump properties for a decade. But he said that since the Times story last year, more have emerged, empowered to speak. He now represents about 40 undocumented people who have worked at Trump properties.

“These workers have been there for many years,” Mr. Romero said. “It’s sad to hear about their firing. But many of them have been able to move on and get better paying jobs. At first when you hear about them, you feel bad. But then you realize that maybe it wasn’t the best environment to work in.”

In an audio recording from one of the firings this week at Trump Winery, a manager told a worker named Omar Miranda that the company had completed a review of immigration paperwork and found that his “did not seem genuine or was insufficient.”