Right now, domestic airlines treat traveling families differently. A handful, such as JetBlue Airways, American Airlines and Alaska Airlines, guarantee that parents can sit next to their children. But on the others, parents are left to pay for more expensive assigned seats or to bank on the good will of strangers.

Recently, President Joe Biden and Transportation Secretary Pete Buttigieg have pressured airlines to implement fee-free family seating, a continuation of the Biden Administration’s push for airlines to be more transparent and accommodating of travelers. President Biden even called on Congress to pass legislation targeting fees for families to sit together.

Instead, the Transportation Department is directly taking aim at them with a new rule proposed today.

“Many airlines still don’t guarantee family seating, which means parents wonder if they’ll have to pay extra just to be seated with their young child,” Mr. Buttigieg said in a statement. “Flying with children is already complicated enough without having to worry about that.”

Here’s what you need to know about the new rule.

It would be free for children age 13 and under to sit next to at least one parent or accompanying adult.

And airlines would need to disclose this policy upfront on online platforms and when travelers call customer service to research or book a fare.

“Next to” means in the same row, when available.

When adjacent seats in the same row are available, airlines will be required to seat parents next to their children, within 48 hours of booking. If this isn’t possible, children could be placed across the aisle or directly in front of or behind a parent or accompanying adult.