The OceanGate CEO was previously warned his experimental Titanic approach could lead to a catastrophic "disaster", according to court documents.
The company's vessel, named Titan, is missing with five passengers on board after losing communication an hour and 45 minutes into its trip to visit the Titanic's wreckage on Sunday.
Pakistani British-based businessman Shahzada Dawood and his 19-year-old son, Sulaiman Dawood, were confirmed to be on the submersible.
British billionaire adventurer Hamish Harding, who is also in the vessel, along with French submersible pilot Paul-Henry Nargeolet, and chief executive and founder of OceanGate Expeditions, Stockton Rush.
A desperate search and rescue operation is underway to try and find the submersible before its oxygen supply runs out on Thursday morning.
And now it's been revealed leaders in the submersible industry sent a letter to Stockton Rush, the OceanGate CEO, warning him that "the current 'experimental approach' of the company could result in problems 'from minor to catastrophic.'
The letter, which was sent by the Manned Underwater Vehicles committee of the Marine Technology Society, is a 60-year-old trade group which promotes ocean technology.
It remains unclear if Mr Rush, or a fellow employee, responded to the letter, and there was no additional information on why the company's approach was considered dangerous, according to the New York Times, who obtained the letter.
In addition, a former employee of OceanGate Expeditions raised "safety concerns" over the vessel but was reportedly "met with hostility" before being sacked, according to court documents.
David Lochridge had raised concerns over "safety and quality control issues regarding the Titan to OceanGate executive management", according to the filings.
In the August 2018 court document, Mr Rush asked Mr Lochridge to conduct a "quality inspection" report on the vessel following the "issues of quality control".
Mr Lochridge "identified numerous issues that posed serious safety concerns" but he was reportedly "met with hostility and denial of access" to necessary documents.
The court documents claim he was worried about a "lack of non-destructive testing performed on the hull of the Titan", and that he "stressed the potential danger to passengers of the Titan as the submersible reached extreme depths".
The company, which charges up to $250,000 for the Titanic wreckage tours, also decided against having the craft 'classed', an industry-wide practice whereby independent inspectors ensure vessels meet accepted technical standards.
Mr Lochridge was later sacked from the company, which he claims was wrongful.
And in 2019, the company said that seeking classification for the submarine would not "ensure that operators adhere to proper operating procedures and decision-making processes – two areas that are much more important for mitigating risks at sea".
The US Coast Guard and Canada are frantically trying to locate the vessel, which is said to have last "pinged" while above the Titanic wreckage.
First District Response Coordinator Captain Jamie Frederick revealed the Coast Guard has already searched 7,600 square miles of ocean, which is the size of Connecticut.
