NEW YORK — The pressure to deliver for online shoppers is on.

With Christmas on a Monday, most retailers have one less day to get packages delivered on time. Some are pushing up their deadlines for standard delivery or free shipping. And after promoting the convenience of buying online with store pickup, retailers are also trying to satisfy lots of customers coming in to collect their orders.

It’s especially important for retailers to hit the mark after some missteps earlier in the season, and because online leader Amazon has the advantage of delivering on Sundays. Research firm StellaService says Dec. 19 is the most popular cutoff date for retailers, two days earlier than last year.

Amazon Prime members, meanwhile, get same-day delivery up until Dec. 24 in 8,000 cities. Retailers have been trying to speed up delivery as they try to replicate the service offered by Amazon. But UPS said this month that some package deliveries were being delayed because of a surge of orders from online shoppers after Thanksgiving. And Walmart said around the same time that more online buying created delays in some orders.

Holiday spending is turning out to be stronger than expected, putting more pressure on stores to get it right.

“I am not very impressed,” said Sheryl Matson of Mount Gilead, Ohio, who has run into problems twice already.

She ordered a PS4 game console on the Kohl’s website two days before Thanksgiving, and the next morning received an email that her order was cancelled. She got on the phone to resolve the issue and got Kohl’s Cash, similar to a gift card, for her troubles. A few days later, she ordered four items on the Kohl’s website for in-store pickup at two places. At one location, one of the three items was missing; at the other store, the product — a digital coin collector– was the wrong color. She says she spent two hours on the phone and $20 in gas money to try to get it fixed. She had to keep the incorrect color, but did receive another $20 in Kohl’s cash.

Now, she’s buying the rest of her gifts at stores: “You see that the merchandise is actually there, instead of relying on their system.”

Retailers are wrapping their arms around e-commerce fulfillment but “are still struggling,” said Alex Vlasto, vice president of marketing at StellaService.