Allegiant Air - BEWARE OF HIDDEN CHARGES Las Vegas Nationwide

 We followed Allegiant's guidelines for traveling with baggage and complied with their 7" x 15" x 16" must fit under seat in front of you.  We had $50 debited out of our checking acct before we landed as Allegiant had card info from when ticket was purchased.  Gate agent decided it didn't comply with their guildelines.  They did not even measure.  Bag was safely stowed under seat in front of us.  Was on hold with Allegiant call center for over 1/2 hr only to be told that anything with wheels regardless of size was going to be charged.  Would have been twenty dollars if paid in advance but at airport $50.  When I said we have always used this bag on Allegiant I was told it is at the gate agent's discretion.  Unbelievable a company can be allowed to operate like this.