Federal investigators have widened their probe of City Hall corruption and union strong-arming to the Boston Grand Prix debacle, putting even more heat on Mayor Martin J. Walsh’s administration, according to sources and the former head of the local race promoters.

John Casey, the Grand Prix CEO whose unexpected cancellation of the IndyCar race triggered a wave of lawsuits by investors and the attorney general, told the Herald he is cooperating with investigators from U.S. Attorney Carmen M. Ortiz’s office as well as the U.S. Department of Labor.

Casey said he has met with the FBI and Labor investigators who are looking into whether the Walsh administration, elected officials or others pressured the promoters to hire union contractors and threatened to withhold permits and approvals if they didn’t go along. But Casey would not get into specifics about what he has told them.

“I reached out based on the issues that we had. They asked for my cooperation along the way and have made great strides,” Casey said.

A Walsh spokeswoman said the city has not received any subpoenas in connection with the IndyCar race and no city officials have been called in for questioning.

Two high-ranking Walsh aides have already been indicted on extortion charges in an alleged conspiracy to force a local music festival, Boston Calling, to hire union stagehands.

Ortiz’s expansion of the investigation into the Grand Prix signals she is far from through in her ongoing probe of the Walsh administration and strong-arm tactics by local unions.

“I think there will be more (indictments) coming,” Casey said.

But the Grand Prix investigation could go further than just union corruption. A number of Walsh insiders and former aides represented the Grand Prix as consultants and lobbyists, and owned equity in the race. The investigation could also draw in numerous state agencies and Baker administration officials who also negotiated agreements with the Boston Grand Prix.

The IndyCar event collapsed amid heated words between Casey and city officials, with the former race CEO saying the administration was too difficult to deal with and threw up last-minute permitting hurdles that killed the event.

Casey also now claims that his cancellation of the race was just “a bluff” and that he met with Walsh days later to try to change the course in the Seaport District to avoid flood zones that are strictly regulated by city and state environmental agencies.

But Casey’s credibility could come into serious question in the investigation. Attorney General Maura Healey has sued him, along with several other vendors and investors, to refund ticket holders who got burned when the Grand Prix went broke.

The Herald has also learned that Casey faces new legal action from a leasing company in Colorado that claims he concocted a scheme to bilk the company out of more than $800,000 by claiming he was using the money to buy new equipment to sell to medical offices.

A Colorado judge this month ruled against Casey and concluded he committed fraud by diverting all the money to shell companies and accounts controlled by him. Casey never showed up to defend himself and the Colorado court ordered him and his wife to pay back more than $1 million in damages.

The Colorado company, Omni Leasing, recently filed a motion in Essex Superior Court in order to collect the money from Casey, who is seeking to dismiss the case.

“We expect to have this whole thing overturned,” he said.