The main concern is that a global supply glut will weigh down prices, which would be a big problem for petrostate budgets.
From the WSJ:
While Saudi Arabia can tolerate lower prices, “there will be some members, like Venezuela, Iran who will struggle at $90,” said Amrita Sen, chief oil analyst at London-based Energy Aspects Ltd. The front month Brent contract for July settled at $102.62 a barrel Monday. Venezuela’s oil minister said on Monday that he would push for a cut in OPEC production if oil falls below $100 a barrel.
We’ve previously shown how falling prices is a concern in the following graph of break-even oil prices for those countries’ budgets.