Emirates is planning to send engineers to monitor Boeing's production lines, Sir Tim Clark, the airline's president has revealed.
The decision comes after a major incident on one of Boeing's 737 MAX 9 planes last month, when a cabin panel blew out during an Alaska Airlines flight.
He had seen a "progressive decline" in Boeing's performance, the Emirates boss told the Financial Times.
"They have got to instil this safety culture which is second to none. They've got to get their manufacturing processes under review so there are no corners cut," he added.
"I’m sure Dave Calhoun and Stan Deal are on that … this is the last chance saloon."
Dave Calhoun is Boeing's chief executive and Stan Deal its commercial head.
This will be the first time that Emirates has decided to send engineers to scrutinise Boeing's production.
The airline is one of the manufacturer's biggest customers, having ordered 95 wide-body Boeing 777 and 787 jets in November, valued at $52 billion (€48.3 billion) according to list prices.
Boeing has not responded specifically to Sir Tim's comments, but has pointed to assurances made by CEO Calhoun last week.
During a fourth-quarter earnings call, Calhoun said he understood why customers were angry, adding: "We will work to earn their confidence."
Other airlines have also expressed doubt over future orders of Boeing planes.
Last month, speaking about Boeing's 737 MAX 10 model, United Airlines CEO Scott Kirby told CNBC: "We're going to at least build a plan that doesn't have the Max 10 in it."
Following the Alaska Airlines incident, the Federal Aviation Authority blocked Boeing from expanding production of its single-aisle 737 MAX, after temporarily grounding the planes.
Boeing announced further delays on Sunday, explaining that some 50 undelivered 737 MAX aeroplanes required more work.
In response to a Reuters request, Boeing confirmed that mis-drilled holes were found in two aircrafts.
"This past Thursday, a supplier notified us of a non-conformance in some 737 fuselages," said Deal, in a letter to Boeing staff.
"I want to thank an employee at the supplier who flagged to his manager that two holes may not have been drilled exactly to our requirements."
"While this potential condition is not an immediate flight safety issue and all 737s can continue operating safely, we currently believe we will have to perform rework on about 50 undelivered aeroplanes," Deal said.
