Checked bags on Southwest and Airtran got a little more expensive today

Southwest Airlines touts its no bag fees policy, but it’s raising checked baggage fees on merger partner AirTran Airways and increasing other fees.

Southwest and AirTran are also raising other fees for overweight, oversized and third checked bags.

The hikes taking effect Wednesday are an indication that low-cost carriers aren’t shying away from adding charges to boost revenue.

AirTran’s fees will now be $25 for a first checked bag and $35 for a second checked bag, up from $20 and $25 and in line with what Delta Air Lines’ charges for domestic flights.

Last month, Southwest began selling at its gates early boarding for a $40 fee and plans to later this year begin charging for no-shows.

Southwest chief executive Gary Kelly told employees it’s an effort “not to extract more money from our customers, but to help avoid fare increases.”

Southwest bought AirTran in 2011 and is gradually converting AirTran operations over to Southwest. In late January, Southwest began linking some of its flights with AirTran’s. The links will roll out through April, opening up many more flight options by allowing connections between the two carriers.

Separately, Southwest marked its first year in Atlanta on Tuesday at AirTran’s former corporate center, where Southwest has a small human resources department, information technology and training, and soon a relocated call center. It will open a small Southwest pilot base in Atlanta in August, while AirTran’s pilot base here will eventually wind down.