Morgan Stanley was hit with a $750 million lawsuit Monday by private-equity firms alleging fraud related to their investment in Brightline Holdings, a high-speed rail company.

The lawsuit, filed in Manhattan by affiliates of Certares Management and Knighthead Capital Management, accused the bank of breach of contract, fraud and breach of the implied covenant of good faith and fair dealing over the restructuring of a deal in which the firms invested in a loan to Brightline, which is also named as a defendant.

Brightline operates a high-speed rail system in South Florida, with a line to Orlando opening this week. The company is also building a 218-mile rail line between Rancho Cucamonga, California, and Las Vegas aimed at bringing high-speed connectivity between the Los Angeles area and Sin City.

Morgan Stanley convinced the companies last year and earlier this year to invest around $281 million by highlighting a “make-whole” provision that would guarantee the investors a certain amount of interest if the loan were repaid ahead of schedule, the plaintiffs alleged. Morgan Stanley misrepresented and concealed terms of the Brightline deal, the plaintiffs asserted.

The plaintiffs alleged Morgan Stanley defrauded them to “position itself for future lucrative investment-banking business with Brightline Holdings and its private-equity owners at Fortress, including through handling municipal debt transactions for Brightline Holdings which could generate sizeable fees for Morgan Stanley,” according to the court documents.

The investors are seeking a court order requiring Brightline to repay them, and to make the make-whole payments.

In a statement to Reuters, Morgan Stanley said "the firm does not believe the claims have merit and will defend itself vigorously."

A Brightline spokesperson told Banking Dive the suit’s claims “are completely baseless and without merit.”

Certares Management and Knighthead Capital Management did not return requests for comment.