The Las Vegas Sun reported Tuesday flight attendants began informational pickets at McCarran International Airport, but were still showing up to work.
Flight attendants for Spirit have been working without a contract for five years and authorized a strike last year.
In spite of that, "We don't want to strike, but we will if that's what it takes for this management to seriously address the issues and concerns of the frontline faces of Spirit Airlines," said Association of Flight Attendants President Todd St. Pierre in a statement.
The union has also asked the National Mediation Board to intervene, the newspaper said.
If a strike is called, it is possible the union would employ a "CHAOS" strike strategy.
"CHAOS" stands for "create havoc around our system." It is a strategy AFA has used in the past, the Sun reported.