The US Transportation Security Administration (TSA) is set to enact new restrictions June 30 limiting the amount of powdered materials international travelers can bring into the cabin on flights bound to the US.

The limits on powders will join other materials including liquids and gels that are also subject to carry-on restrictions stemming from concerns about aviation security and terrorism.

The new rules will restrict the amount of powders travelers can pack in their carry-on luggage to 350 milliliters—roughly 12 ounces, or the size of a soda can. The limits going in place for international travelers have applied to US fliers since July 2017, when TSA enacted heightened screening procedures for US passengers’ carry-on luggage.

Powders exceeding 350 milliliters will be subject to secondary screening, as opposed to a blanket ban. If screening procedures at central or main checkpoints are unable to verify the materials are safe, passengers will be instructed to discard or place them in checked baggage.

TSA Spokesman Michael England told ATW the new measures are part of TSA’s efforts to “stay ahead of threats, keep passengers safe and constantly increase capabilities through a layered approach to security.” He cited a range of powders, including fentanyl and oleoresin capsicum (known as pepper powder or pepper spray) that could potentially be used to “irritate or harm aircraft passengers and aircrew if released during flight.”

“TSA is working with international partners to align global aviation security standards. Improvised explosive devices still pose the greatest threat to commercial aviation,” England said.

The new requirements come just two weeks after US Customs and Border Protection (CBP) and TSA initiated the Air Cargo Advance Screening (ACAS) program, which requires the submission of advanced air cargo information on all international shipments arriving in the US. Previously a voluntary process, CBP called ACAS a “necessary measure as the Department of Homeland Security (DHS) continues to raise the baseline on aviation security worldwide.”

Ben Goldstein,