DALLAS — For the second time in less than two weeks, major US airlines are raising fares.

United Airlines confirmed Thursday that it increased prices on many domestic flights by $10 per round trip.

JPMorgan airline analyst Jamie Baker said, however, that he will be surprised if Southwest Airlines follows suit, coming only two weeks after airlines raised base fares by $4 to $10 per round-trip ticket.

If discounters refuse to go along, United could be forced to retreat.

Also, airlines often undercut price increases by running fare sales. For example, Delta Air Lines boasted about weekly specials in an e-mail to customers on Tuesday.