Hawai'i's interisland airfare war is getting hotter.

Go! airlines has cut its one-way interisland fares to $29, spurring Hawaiian Airlines to do the same.

And Aloha Airlines spokesman Stu Glauberman said the carrier "will be competitive" and plans to make an announcement on fares this week.

The go! price cut comes a month after the Phoenix-based carrier, the underdog in the Islands, sparked an interisland fare war with its $39 one-way tickets. Both Hawaiian Airlines and Aloha Airlines matched the $39 fares. Aloha also handed out free round-trip tickets to 1,000 customers on June 9 — go! airlines' launch date in Hawai'i.

The $29 fares are good for travel between Honolulu and Hilo, Hawai'i; Kailua, Hawai'i; Lihu'e, Kaua'i; and Kahului, Maui. Tickets must be purchased by tomorrow, and used anytime before Sept. 30.

"The mission of go! is to bring friends, families and business people together by offering exceptional service at the lowest possible price," Mesa Air Group Chairman and Chief Executive Officer Jonathan Ornstein said in a news release.

"The response to go! has been tremendous, and we want to continue to reinforce our position as Hawai'i's low fare carrier."

Mesa Air Group owns go!, along with Mesa Airlines. The company was founded in New Mexico in 1982 and has about 5,000 employees.

Hawaiian Airlines spokesman Keoni Wagner said $29 fares will be available on the company's Web site today. They must be purchased by tomorrow and are good for travel through Sept. 30, he said. He declined to comment further on go!'s decision to cut fares.

Glauberman pointed out Aloha Airlines was offering $29 fares last week.

Several thousand tickets were sold at that price, he said. He added that a similar fare will likely be available on the company's Web site sometime this week.

"I can't tell you if we will be matching," he said.

Reach Mary Vorsino at mvorsino@honoluluadvertiser.com.