The Singapore-listed shipbuilder confirmed on Friday that two customers had pulled orders for six 37,500-dwt bulkers worth $160m.
JES said one owner, who had eight bulkers on order, had cancelled four, while a second owner with four ships of the same size had cancelled two.
Deposit payments for the six cancelled vessels have been pushed on to the remaining newbuildings the two companies have on order at JES.
The unnamed duo have also pushed back the deliveries of a further four and two handysize bulkers respectively by between two and four months.
Pancoast Trading and Tankerska Plovidba are known to have had eight and four 37,500-dwt bulkers on order at the shipbuilder respectively.
JES figures released last year show the two shipowners to be the only owners with bulkers of this size on order at the yard.
Pancoast Trading’s eight ships were due for delivery between 2008 and 2010, while those of Tankerska Plovidba were due between 2008 and 2009.