On July 20 he tweeted that he had received approval to build a train tunnel for his Hyperloop - a system of transportation pods propelled through vacuum tubes at up to 1200 kilometres per hour - from NY to Washington, DC.
Some city representatives, however, say no such talks have occurred.
"You can build a tremendous amount underground with the right boring technology on Mars, so I do think there's some overlap in that technology-development arena", Musk said.
Within an hour of sending his first Hyperloop tweet, Musk followed up with a few more details.
That leaves us with the million dollar question: Who gave Musk the green light?More news: KBW downgrades Goldman, calls it "show-me" stock
A U.S. Transportation Department spokesperson was not immediately available to comment.
Shortly after Musk's tweet, de Blasio's press secretary Eric Phillips responded to Musk's announcement with his own tweet suggesting the mayor knows nothing of the verbal approval. The Boring Company's main goal is to construct tunnel networks beneath (and, eventually, between) traffic-choked cities such as Los Angeles, enabling speedier travel. The Boring Company is Musk's tunneling venture.
Musk said during a TED conference in April that his tunneling company ties in closely with the hyperloop, since both require vacuum-sealed tunnels.
Musk said hyperloop tunnels could ferry people, cars and even bikes from NY to Washington in 29 minutes.
The hyperloop would be built underground, says Musk, and would allow travel between NYC and D.C.in just 29 minutes. If the project is actually approved, construction will begin in conjunction with the company's other talked-about project: underground tunnels in L.A. that aim to relieve vehicular congestion. Garcetti said he was considering using Musk's tunnel to support a high-speed rail connection. The company is working toward building a tunnel from Los Angeles International Airport to Culver City, Santa Monica, Westwood and Sherman Oaks. CNBC asked Musk's Boring Company to clarify which government agency or agencies have told Musk they approve of his Hyperloop plan, but have not yet received a response.