Feb 23 (Reuters) - United Airlines said on Friday it was raising its checked bag fees for customers traveling in North America, days after American Airlines announced a similar increase.

Carriers are grappling with higher maintenance and labor contract costs amid weakening pricing power in the U.S. domestic market.

United passengers flying economy in the United States after Feb. 24 will pay $40 for their first checked bag, or $35 if they pay in advance. A second checked bag will cost $50 at the airport and $45 in advance.

The price increase comes four years after United raised its prices for checked bags at airports by $5 to $35, charging a steady $30 if travelers bought the service in advance.

Earlier this week, American Airlines raised its fees for the first checked bag to $35 if the service was booked in advance online, or $40 at the airport. (Reporting by Kannaki Deka in Bengaluru; Editing by Pooja Desai)