TAMPA — Frontier Airlines is the fastest-growing airline at Tampa International Airport, where its jets are painted with a company menagerie of iconic wildlife: bears, foxes, owls and big-horn sheep.

The Denver-based airline says its no-frills, low-budget fares make air travel possible for students, retirees on fixed incomes and first-time fliers.

But this week, two of the airline's pilots arrived at TIA in a 37-foot recreational vehicle painted Frontier-style with a hawk in flight, talons extended, and a more ominous message for those budget-conscious customers:

FRONTIER PILOTS: 100% READY TO STRIKE

No strike has been scheduled, and wouldn't be until a federal mediator declared negotiations to be at an impasse — something the pilots have requested — and a 30-day waiting period passes.

But Frontier Capt. Alan Christie said the airline's 1,280 pilots are ready to strike over low pay, restrictive work rules, loss of retirement and vacation benefits and what he describes as the airline's don't-give-an-inch approach to contract negotiations.

"Basically, they're looking to extract even more money from the pilots despite the fact that the pilots are paid 50 percent less than virtually every other Airbus operator in the country," said Christie, a spokesman for the Airline Pilots Association, International, which represents pilots at 34 airlines.

New Frontier pilots can expect to start at $34,000 to $35,000 a year, he said. At JetBlue, which recently negotiated a contract, he said pilots start at $65,000 to $70,000 a year. Switching to another airline means a loss of seniority and pay for pilots, he said, creating a disincentive to changing jobs, especially for later-career pilots.

So the "strike bus" is meant to send a message to prospective Frontier passengers: Your ticket could be worthless if a strike cancels your flight.

In Tampa, Frontier's passenger count has more than doubled in two years to 1 million passengers a year, with bookings rising 83 percent in the past year. Frontier has a fleet of 80 jets, but has 200 new Airbus 320neo jets on order.

ONE GROWTH SPURT IN 2017: Frontier Airlines launches flights out of Tampa airport to 11 new destinations

AND ANOTHER THIS YEAR: Frontier Airlines expands service from Tampa to six cities

"The aggressive growth strategy that Frontier is looking to undertake is in serious jeopardy of stalling out unless they come up with a market-rate agreement with the pilots," Christie said.

In response, a Frontier spokesman said the airline is operating as usual.

"We are engaged in negotiations with our pilots for a new contract and continue to exchange proposals under the guidance of the National Mediation Board," Frontier director of corporate communications Jonathan Freed said in an email. "We look forward to working toward an agreement that is fair, sustainable, and provides security for everyone."

Earlier this year, the pilots union and Frontier went to arbitration over a union grievance about Frontier's bargaining. Documents later filed in federal court in Illinois detail the dispute:

In 2011, Frontier was struggling and facing reorganization or liquidation in bankruptcy court. The pilots agreed to give up $53 million in wages and other benefits. They also agreed to postpone a chance to amend the contract for two years until 2017.

Profits have since improved, and some pay cuts were rolled back in 2015 and 2016. Now that the union can negotiate to amend the contract, the question of pay raises based on Frontier's business conditions has become a sticking point.

The union pointed to information reported to the U.S. Department of Transportation showing that Frontier had a profit margin of 15 percent in 2014, rising to 18 percent in 2015.

"We've made more money the last 10 months," Frontier's CEO said in a 2016 newsletter quoted by the union, than "in the previous 10 years combined."

Further, the union pointed out that Frontier had paid bonuses to executives and dividends to shareholders of $108 million in 2016 and $165 million in 2017.

The union argued that granting the pilots' proposal for a $28 million pay increase would drop Frontier pre-tax profit margin from 18.4 percent to 16.6 percent.

Frontier countered that:

• There was no evidence the contract was negotiated to require the company to grant pilots a pay increase when it became profitable.

• It offered to increase pilot pay in exchange for money-saving changes to vacation rules.

• Relevant business conditions from its perspective include the risk that union negotiations could result in higher costs for Frontier without any savings in pilot productivity or efficiency.

• Its pre-tax profit margins are the lowest in the ultra low-cost carrier market. Its passenger revenue per seat-mile has not grown. And its average cost per seat-mile is higher than Spirit's, its chief competitor.

The arbitrator found that Frontier had not bargained in good faith. Soon after, pilots voted in favor of a strike.

Christie said pilots hope Frontier — led by its customers, if necessary — conclude that the airline is better-served by paying its pilots better, but he and his colleagues are ready to walk off the job if that's what it takes. That's why they're taking the strike bus to 25 cities, including, this week, Orlando, Jacksonville and Tampa.

"We don't want a strike," he said. "We want Frontier to be successful, and we have given up a lot ... to make sure the airline stayed in business. We are not looking for a market-leading contract. We are just looking to be paid what the going rate is for pilots in the marketplace."

MORE: Go here for more Business News

Contact Richard Danielson at rdanielson@tampabay.com or (813) 226-3403. Follow @Danielson_Times