If the White House decertifies the Iran deal, RBC Capital Markets is warning investors that oil prices could jump.

Helima Croft, the firm's global head of commodity strategy, is watching next Thursday, October 12 very closely. That's the day when President Donald Trump is expected to deliver a key speech on Iran policy.

There's speculation that Trump will move to unravel the international deal, signed under President Barack Obama, that curbs Iran's nuclear program.

"It's a very significant development that could happen next week," Croft said on CNBC's "Trading Nation" this week.

An official told Reuters this week, speaking on the condition of anonymity, that Trump is also expected to introduce a broader U.S. strategy that would be more confrontational with Iran.

"The market, I think, will be concerned that we can get a return of the sanctions that required importing countries to make significant reductions in their Iranian crude imports every six months, and which bars foreign firms from investing in the Iranian upstream sector," noted Croft.

A National Iran Oil Company official told CNBC on Sept. 25 that it's exporting about 2.2 million barrels a day — a year after U.N. economic sanctions were lifted last year.

Fresh sanctions could put demand in a delicate situation.

"To really move significantly higher, what we really need to see is clear indications that sanctions are coming back, because right now there's a view out there that the 'U.S. just goes at it alone on sanctions. It won't matter,'" Croft added.

But the prospect of an increased demand due to falling supply doesn't appear to be affecting Wall Street.

West Texas Intermediate (WTI) crude fell by 2.95 percent to close at $49.29 a barrel on Friday, breaking a four-week win streak. It was the commodity's biggest weekly loss since March 10. Friday's loss happened on profit-taking and the return of oversupply concerns.

RBC's year-end forecast calls for U.S. oil to end the year in the low $50s.

"What matters is how much does the United States government, the White House in particular, want to force foreign firms out of Iran. If they want to force them out, they can always threaten to lock them out of U.S. capital markets. And that's a pretty big stick," Croft said.