Many families who own static mobile homes at the site near Pickering rent them out to other guests and were previously paying £1,000 per year to be allowed to do so.
This has now been raised to £2,000 while the annual ground rent per unit has also gone up by £200.
Owners claim that no prior consultation took place before an email was sent out confirming the price increases and a full explanation or breakdown of the decision was not given.
They say they are struggling to understand how the park can justify the additional costs when most owners handle all of the administration and maintenance themselves and staff involvement is minimal.
Kayleigh Meah, from County Durham, has owned her caravan for five years and describes it as an 'escape' for her husband and two childen, who are disabled. She now fears she will be unable to rent it for holiday bookings as she will have to increase the charge to one which is unaffordable for many families.
"It's caused uproar - there has been no consultation about this increase. The park already do very little for us as the owners handle most things themselves.
"The prices we charge guests are already high, and now people will be able to go abroad for the same money, so we can't really put them up any higher. It has a domino effect.
"Some people own up to five caravans, so they are faced with paying an extra £10,000. We do the inspections, testing, gas bottle replacements and other maintenance ourselves. They've only recently started cutting the grass and many owners still do that themselves too. The guests have to buy passes for the theme park separately too, as we can't include them in the booking charge.
"Everyone wants to complain - we are confused, scared and many are wanting to sell. The manager is nowhere to be seen. Nobody is going to want to buy our caravans.
"The park already makes so much revenue from us. It's just not feasible or manageable, and we are questioning whether it is even legal. We were already wondering why we were paying the original £1,000 subletting fee."
Also affected by the charge is Mike Horan, who owns three caravans and manages a further 13 on behalf of other owners.
"This will cost us over £16,000 just on the extra cost to sublet. I will be forced to put prices up which will have a detrimental effect due to the prices that Flamingo Land charge to stay in their own caravans during the low season. We are already unable to compete with them.
"The Holiday Park Action Group have said they have broken their side of the contract and they will be taking it further on our behalf."
In response, Flamingo Land Resort's management pointed out that many holiday villages around the UK do not allow caravan owners to rent their units to others independently.
They added that the price increases are to cover rising operational costs in the resort, including investment in new and upgraded rides and improved roads.
A statement from chief executive Gordon Gibb read: "We always strive to improve standards at Flamingo Land and our decision to increase the cost of our sublet certificate is in line with this strategy.
"Aside from the significant increases in costs that we are enduring as a business in wages, supplies and utilities we are also constantly developing our attraction. Specifically installing a 10 inversion rollercoaster, continued infrastructure improvements, and most importantly, keeping standards of our animal care at a world class level.
"I would also point out that Flamingo Land's revenue is also used to finance our critically important conservation work in Africa through our UFP programme, animal release initiatives and reforesting Africa.
"The income generated by our subletters for themselves is far more significant than any competing caravan park in the UK and I would politely suggest that if any of our subletting caravan owners feel they can financially improve their incomes on any other operation that they would have already done so, or will have Flamingo Land's full support in releasing their caravans to an alternative site if required.
"The price rise is £1,000 over a full season which is the equivalent to a subletting customer passing on a £30 (circa) increase to each week-long booking.
"All of our corporate competitors manage sublet business for their caravan owners and charge accordingly. On average, a week's stay would be charged to the customer by the park for £700 (circa) and, based on my research, the caravan owner would receive £260 (circa). Flamingo Land allows all of its caravan owners to keep their income from all of their customers, subject to paying for a sublet certificate which is now priced at £2,000.
"Flamingo Land continues to be fabulous value and even after levelling-up our pricing policy to our competitors we still believe that we are by far the best holiday village in the UK from a value and quality perspective."
Mr Gibb added that David Hunter had only recently been appointed to the post of general manager, but lives on the site and is available to speak to owners who have concerns.