President Donald Trump is threatening to "decertify" the 2015 agreement that froze Iran's nuclear program — and if he follows through, it could hurt Boeing.

The U.S. aircraft maker has an agreement to sell 80 new planes to Iran Air and another 30 to Iranian carrier Aseman. The total value of those deals is about $20 billion dollars.

Boeing is the best performing stock in the Dow Jones Industrial Average over the last year, doubling the performance of its nearest competitor. "If Boeing isn't able to deliver the airplanes to Iran, it probably would have some impact on the stock," said Cowen aerospace analyst Cai von Rumohr.

Despite any potential problem, he upped his price target on the stock last week to $315 dollars a share, almost 25 percent higher than it is now. "This could be a bigger issue for 2019 than for 2018," he said.

The reason is that Boeing is oversold for next year, meaning the manufacturing giant would likely be able to sell those planes to another carrier if the Iran deal falls through. However, according to von Rumohr, Boeing has sold just 90 percent of its 2019 inventory, meaning it could get stuck with extra planes.

If President Trump does decide to "decertify," the nuclear deal — which would essentially remove the United States from the agreement — it's still unclear what would happen after that. Decertification would not necessarily mean all business ties are off. Europe and Asia have growing business ties with Iran, and officials from both continents are urging the U.S. to stay in the deal.

However reports quoting Iran's foreign minister Mohammad Zarif late last week stated that if the U.S. leaves the deal, Iran could also exit, meaning the situation could revert to where it stood before the landmark agreement was signed in 2015.