As bricks-and-mortar retailers attempt to attract more customers and make more sales, they are increasingly courting online shoppers. But all of those two-day shipping services and other free shipping guarantees are putting pressure on delivery companies, and that could be a big problem, according to the top executive at JCPenney.

The Street reports that JCPenney CEO Marvin Ellison believes the biggest obstacle for e-commerce retailers will be actually getting products to customers.