Chicago-based aerospace giant Boeing will temporarily stop producing its beleaguered 737 MAX planes next month, as it has run into a snag preventing it from getting its planes back in the air.

The 737 MAX is Boeing's most-important jet, but it has been grounded since March after crashes in Indonesia and Ethiopia that killed a total of 346 people.  Almost 400 MAX 8s are in the world's aviation fleet, with another 400 units produced since the crashes and waiting in storage yards.  

Boeing has been pushing regulators to allow it to put the jets back into service, but the United States Federal Aviation Administration (FAA) told the plane-maker that its expectations are unrealistic - and that it has no set time frame for when work to re-certify the MAX to fly will be completed.

For now, Boeing says it will not lay-off any of the 12,000 MAX 8 workers, and will instead send them to work on other products. 

"We believe this decision is least disruptive to maintaining long-term production system and supply chain health," the company said in a statement.

But the suspension is likely to have a profound impact on Boeing's supply chain.  That includes big companies such as Spirit Aerosystems which makes fuselages for the planes, and General Electric which makes engines for the 737 MAX in a joint venture with France's Safran SA.  Smaller companies could be hit hardest, because they have less cash on hand to withstand a lengthy shutdown.