WASHINGTON (Reuters) -The U.S. Department of Transportation said on Thursday it is proposing barring U.S. and foreign airlines from charging fees to seat families with young children together on a flight if adjacent seats are available during booking.

The Biden administration said in February 2023 it planned to write regulations barring the fees as officials pressured airlines to voluntarily not charge them.

In May, Congress passed legislation that President Joe Biden signed into law directing a ban on the practice.

Biden has repeatedly clashed with air carriers, calling for new, stricter consumer rules and criticizing them for imposing fees.

His administration has also aggressively moved to block further consolidation in the passenger airline industry, including successfully blocking a tie-up between JetBlue Airways ( JBLU ) and Spirit Airlines ( SAVE ) and quashing an alliance between JetBlue ( JBLU ) and American Airlines ( AAL ).

The DOT launched a family seating dashboard in March 2023 that shows four airlines -- Alaska Airlines, American, Frontier, and JetBlue ( JBLU ) -- have committed to guaranteeing family seating without separate fees, the DOT said.

All other large domestic carriers have policies attempting to seat families together but do not guarantee it, the DOT said.

The proposal bars airlines from charging fees to assign seats to children to sit next to their parents on U.S. flights. Where that is not possible, to provide adjacent seating for multiple young children, airlines would be required to seat them across the aisle from, in front of, or behind a parent.

The DOT would require refunds or free rebooking when adjacent family seating is not available if passengers chose not to take that flight. Airlines could face civil penalties if they did not comply.

Earlier this week, a U.S. appeals court blocked the DOT's new rule on upfront disclosure of airline fees pending a full review of the regulation.

Biden in May 2023 said his administration would propose new rules requiring airlines to compensate passengers with cash for significant flight delays or cancellations when the carriers are responsible but the DOT still has not released a proposal.