Democratic presidential candidate Hillary Clinton made a surprise appearance at a union rally held outside of Donald Trump's hotel in Las Vegas Monday evening, where she bashed the GOP presidential front-runner and showed her support for labor workers.

At the rally, Clinton joined about 500 members of the Culinary Workers Union in Nevada who were demanding that Trump allow workers at the Trump International Hotel to unionize, reports CNN.

"You have to say...'no' to efforts to prevent you from organizing, to prevent you from having the kind of working conditions you deserve, the kind of wages that are going to give you a living wage," Clinton said at the rally. "And that means saying no to Donald Trump."

"Some people think Mr. Trump is entertaining. But I don't think it's entertaining when somebody insults immigrants, insults women. That is just unacceptable behavior," she added. "When we're here together in solidarity to organize, we also want to send a message to Mr. Trump: That if you're going to run for president, then you should represent all the people of the United States, and that includes hard-working people."

During the rally, a hotel worker who has been working ss a guest room attendant at Trump International for 6 years named Maria Jaramillo talked about her desire to join a union.

"Mr. Trump said, 'Make America great again.' The Trump workers say, 'Start here!'" Jaramillo said to loud applause, reported The Huffington Post.

On the other hand, Eric Trump, an executive vice president at the Trump organization and the son of the presidential candidate, insisted that the hotel workers are largely happy.

"For years the union in Las Vegas has been trying to unionize this hotel, and they have been incredibly unsuccessful. We have an incredible group of employees who have categorically rejected unionization," he said, according to NBC News.

Clinton's rally visit came just a day before she will participate in the first Democratic presidential debate at the Wynn hotel on Tuesday along with Vermont Sen. Bernie Sanders and three other candidates.

Watch footage of the rally below.