Millennials have been blamed for “killing off” traditional mainstays like homeownership and traditional taxi systems, but e-commerce might just be one where they have significant pull in pushing it forward.

A new study reports that delivery speed is the biggest concern of online shoppers, while over a third of millennials are frustrated with slow delivery times. In the U.S. alone, that represents more than 27 million people. In fact, younger consumers were the most critical with over 35 percent reporting that they frequently deal with challenges receiving online orders.

More than 3,000 consumers were surveyed in the U.S., UK, and Canada to better understand growing challenges in e-commerce, retail fulfillment, and delivery trends.

With growing consumer demand for express and same-day delivery for everything from flower arrangements to furniture, this percentage could continue to rise.

At first glance, this feels like a loss for retailers — a large percentage of a growing consumer base is complaining. And the change to meet that demand simply doesn’t happen overnight. Amazon has set the stage with same-day delivery, owning nearly 50% of e-commerce sales in 2017. Retailers are now looking for ways to catch up.

But a closer look reveals a huge opportunity for e-commerce companies.  Understanding consumer frustrations and subsequently acting on them gives retailers an opportunity to build omnichannel programs that set themselves apart from the competition. And over time, hopefully, increase its market share in e-commerce sales.

It’s no secret that delivery is a huge player in the ongoing e-commerce war. If delivery cost, speed, and reliability are major buying factors for the growing millennial consumer base, it only makes sense for retailers to significantly invest in that area.

That’s why many retailers are turning to alternative shipping services to meet the demand for next-day, same-day, and even two-hour delivery. For both small businesses and enterprises, many are turning to a collaborative delivery model — tapping into a fleet of vehicles already on the road — for a flexible, scalable delivery solution.

Not only are many discovering that cost-effective same-day delivery from the store can be a reality, but many are seeing the bottom-line impacts of increased sales, customer satisfaction and saving potentially abandoned sales.

This survey comes on the heels of a global study that reports nearly 90% of retailers expect to use crowdsourced delivery within a decade to meet delivery demand.