And he lumped Cruz in with Democratic presidential candidate Hillary Clinton.
"I know the guys at Goldman Sachs. They have total, total control over him. Just like they have total control over Hillary Clinton," Trump said of Cruz, whom the real estate mogul also called a "total fraud" and "the biggest liar I've ever seen."
Trump made the claim by pointing to two loans Cruz received to fund his Senate campaign, including one from Goldman Sachs, which Cruz failed to properly disclose until a January report revealed the omission.
Trump added that "Cruz is totally controlled by the oil companies," pointing to political contributions Cruz has received.
In a statement, Rick Tyler, Cruz's communications director, fired back.
"Cruz's wife, Heidi, was an employee of Goldman Sachs. The Cruz's loan was exactly the same loan any other employee would qualify for and they borrowed the money against their own assets so there was no special deal," Tyler said.
He added: "So does Trump offer any evidence for his false assertions? Any?"
Trump's sharpened attacks come just a day before Republican voters head to the polls Saturday in South Carolina, where Trump is leading in the polls. Several polls show Trump with a double-digit lead over Cruz, but an NBC/Wall Street Journal poll published
Friday shows Cruz coming within 5 points of Trump.
The dig accusing Cruz of being controlled by special interests is one Trump has leveled against Cruz and his other political rivals throughout his campaign, which Trump uses to point to his own independence from big-moneyed interests.
"They have no control over Donald Trump. I don't want their money. I don't need their money," Trump said Friday, pointing to Goldman Sachs.
Trump's campaign does accept individual donations from supporters, but his campaign's coffers are largely filled with the candidate's own money and Trump has also disavowed any super PACs from supporting him -- a point Trump has increasingly stressed on the campaign trail.
In the wake of his second-place finish in Iowa, Trump suggested that voters perhaps did not sufficiently appreciate his "self-funding."
But during an event on Thursday, Trump put more faith in voters' concern for the influence of special interests in the political campaign.
"I think it resonates with voters," Trump said.