Sen. Elizabeth Warren reignited her feud with Securities and Exchange Commission Chair Mary Jo White — and this time she’s dragging billionaire hedgie Steven Cohen into the middle of it.

Warren (D-Mass.) on Thursday ripped into the SEC for allowing the former SAC Capital chieftain to start a new hedge fund firm just two months after he was barred from managing outside money until 2018.

Cohen’s move has made a “mockery of the SEC’s core mission to protect investors,” Warren wrote in an open letter to White.

In January, Cohen agreed to a two-year ban on managing outside money to resolve allegations of insider trading at his former firm. He didn’t admit to any wrongdoing as part of his agreement with the SEC.

SAC Capital had already paid $1.8 billion to settle civil and criminal charges tied to the long-running investigation.

After the plea deal, Cohen converted SAC into an $11 billion “family office,” Point72 Asset Management, which mostly manages his huge personal fortune.

Warren’s letter revives a long-simmering tension between two of Washington’s most powerful women.

In June, Warren said White’s tenure atop the SEC was “extremely disappointing” and accused the regulator of lying to her about when she would roll out a rule publicizing executive compensation.

White said Warren had committed a “mischaracterization” of her statements.

The SEC pushed back against Warren’s letter on Thursday, saying it wouldn’t let Cohen out from under the microscope.

“Under the settlement’s significant requirements, the SEC will scrutinize his trading activity closely going forward to protect investors,” Andrew Ceresney, the SEC’s head of enforcement, said in a statement.

Five weeks after he agreed to the two-year ban, Cohen filed paperwork to start a new firm, called Stamford Harbor Capital, that can raise funds from other investors before his sanctions are lifted.

Cohen insists he isn’t skirting the settlement because — even though he owns the new firm — he won’t actually manage any of the money.

Indeed, the SEC settlement includes a provision that allows Cohen to raise outside money so long as he doesn’t have a supervisory role.

“The SEC imposed clear conditions in the settlement,” said a spokeswoman for Cohen’s Point72.

“We are not going to manage one dollar of outside money prior to January 1, 2018. We are fully meeting, and continue to meet, the letter and spirit of the agreement.”

But Warren believes the SEC fell down on the job. She wants the agency to “put procedures in place that ensure that future settlement agreements cannot be so easily undermined,” according to her letter.