Florida Sen. Marco Rubio and Texas Sen. Ted Cruz came out of the gate swinging at Donald Trump in Thursday night’s Republican presidential debate in Houston. The two senators criticized Trump for hiring undocumented immigrants for jobs they said could have otherwise gone to American citizens.

After the candidates each talked about their stances on immigration and emphasized how tough they would be on deporting undocumented immigrants, Rubio brought up Trump’s history with hiring immigrants at one of his companies. Last summer when Trump first entered the race, immigrants working at his hotel’s construction site came into the spotlight, but Rubio was correct that the New York businessman has come under fire for hiring immigrants in the past.

“Donald Trump Polish workers -- Google it,” Rubio said, referring to undocumented immigrants who were employed to construct Trump Tower.

Thirty-five years ago, more than 200 undocumented immigrants built the iconic Trump Tower in New York City, the Daily Beast reported last year. As Rubio asserted, the immigrants came from Poland, and it turns out they were not too happy with their employer.

In a civil suit in federal court, testimony showed the laborers were paid $5 an hour or less, and there were other complaints about their pay as well. There was some question about whether Trump knew what was going on with the Polish workers, but an appeals court ruled that if they did not know, “they should have known.”

During the debate, Trump shot back at Rubio, saying he had more business sense than the Florida senator. “I've hired thousands of workers, you haven't hired any,” Trump said.

Cruz joined in the fight, hitting Trump on his seriousness over immigration.

“Anybody who really cared about illegal immigration wouldn’t be hiring illegal immigrants,” Cruz said.

Trump was not putting up with the criticisms, however. The candidates yelled over each other and the businessman added, “You don’t know anything about business.”

Thursday’s debate marked the last chance for the five remaining Republican candidates to face off before the all-important primary contests on Super Tuesday next week. It was expected to be an intense showdown, as both Cruz and Rubio ramped up their attacks against Trump this week, following his overwhelming win in Nevada's Republican caucus on Tuesday.

Now that Trump has won three primary contests in a row, the GOP establishment has started to significantly changed its tune, with many political analysts and media members saying that the New York billionaire is on his way to collecting the number of delegates needed to secure his party’s nomination. However, establishment politicians have also taken to attacking Trump in a sign that they are hoping another candidate — most likely Rubio — can still stop his progress.

Former Republican presidential nominee Mitt Romney struck out at Trump this week , suggesting that the front-runner has a “bombshell” hidden in his tax returns, and calling for Trump to release his returns to the public. Trump responded in typical fashion, tweeting that the former Massachusetts governor was “one of the dumbest and worst candidates” in GOP history. During Romney’s 2012 White House bid, he was on the receiving end of similar criticisms regarding his taxes and business record.

Another contentious topic ahead of Thursday night’s debate was the idea that Trump carried the Latino vote in Nevada, according to entrance polls, despite both Cruz and Rubio having Hispanic backgrounds. Trump bragged about this in his victory speech Tuesday night, and the issue of Hispanic support could be important for states like Texas and Florida, which both Cruz and Rubio are hoping to win. As of Thursday, Trump maintained his lead nationally, sitting at 33.2 percent in the Real Clear Politics average of polls, while he also stood well ahead of Rubio in Florida but trailed Cruz in Texas polling.