Sun Country Airlines, aiming to boost revenue and reshape passenger habits, announced new fees for luggage and seat assignments Monday.

The options impose new choices for customers and introduce some complexity. The seat-related fees, for instance, will vary depending on the time of year, length of the flight and whether it's an aisle, middle or window seat.

With the move, Sun Country moves a step closer to the pricing structure of ultralow cost carriers, which impose fees for services that are standard on other airlines. Executives said they're not going quite as far as some of those airlines, however, and that some of the fees would likely improve the flying experience.

"We are doing what we said we would," Jude Bricker, Sun Country's chief executive, said, referring to signals the company sent in recent weeks about the change. "And what we are doing at Sun Country that's a little bit different is we are bundling the fees."

Passengers who book tickets for Sun Country flights will soon select between three baggage "bundles" depending on whether they want to carry on, check or not bring luggage on a flight.

The highest fee affects those who bring their roller suitcase or duffel bag into the airplane cabin to store in an overhead bin. This carry-on bundle, which the airline calls the "store & go" bundle, is $30 for flights within the Lower 48 states and $35 for all other destinations. These customers will also be allowed one personal item. If a customer waits until arriving at the airport to select this option, the price increases to $40.

Passengers who prefer to check their bags will be charged a more modest $20 for flights within the U.S. mainland and $25 for all other destinations.

The third option, "the grab & go" bundle, is for the budget traveler. This passenger is allowed one personal item, like a purse or small backpack, which must fit beneath the seat.

Sun Country currently charges only for checked luggage. The new scheme is designed to reward travelers who check their bags.

The popularity of carry-on luggage soared after airlines began imposing fees for checked bags. Passengers sought to avoid the extra cost while also reducing the risk of a lost bag. This caused problems for airlines in the boarding area and aboard the plane. The abundance of travelers carrying large luggage into the cabin often leads to departure delays.

Bricker said this will speed up the boarding and deplaning processes by encouraging people to change their behavior. Bricker, who joined Sun Country in July, said Allegiant Air saw a six-minute improvement in turnover time with a similar policy when he was chief operating officer there. "There's a limited number of bags that will be sold for the overhead bin space … so it's also a way to guarantee we will have enough space," Bricker said.

In September, Sun Country's leaders said they would be changing the bag-fee structure and implementing other changes at the airline.

Beginning Wednesday, customers booking online for travel in 2018 will face another choice: where do they want to sit on the plane and how much are they willing to pay for that choice. Seat selection will range from $2 to $35 depending on location, time of year and flight length. As a way of rewarding higher-paying customers, Sun Country will give passengers who book either the "store & go" or "check & go" bundles a $5 discount on their seat selection.

Bricker says these bundles are a way to give customers control over paying for only what they value. By removing the cost of some amenities, Bricker said base ticket prices should come down though he declined to say by how much. "There's going to be a correlation between the price of the fees and the price of the base fare," he said.

The old fee structure still applies to customers with existing bookings. The new structure affects those who book reservations on or after Oct. 25 for flights taken on or after Jan. 19, 2018.

Ufly Rewards members who have a Sun Country credit card or those who purchase a vacation package will get a free checked bag. Elite members will get any of the bundles for free and will get two free bags for themselves and anyone else on their reservation.