The Ramada in Portrush, which was owned by the Kennedy family, went into administration on Thursday.
Nama has appointed receivers to the Kennedys' other property assets in relation to a £48m debt.
East Londonderry MP Gregory Campbell said he feared the move could see the hotel sold at a significant discount.
He said it could mark the start of a so-called fire sale by Nama of properties it holds in NI.
Nama has always maintained it is not in its interests to have a fire sale in Northern Ireland.
So far, there has been no comment from the agency.
The news was met with shock by the owners and local politicians.
The 69-bedroom hotel has an annual turnover of £2.2m and has won several awards.
The owners were informed on Thursday afternoon that administrators had been appointed and will now run the hotel.
The 50 full-time and part-time staff have been informed.
The owners said that despite several requests, they had been unable to meet with Nama over the past few months.
In a statement on the hotel's Facebook site, Alistair Kennedy said the business would trade as normal.
"We have been assured that all bookings and reservations are safe," he said.
"The Kennedy family who have owned and operated the hotel for the past 11 years would like to thank all our customers and friends for the support and custom they have given us over that period of time."
Mr Kennedy said he hoped customers would continue to support the hotel's staff "during what is obviously going to be a very difficult period for all involved".
In an interview with the BBC, Mr Kennedy said that on Tuesday the group had been served with a demand by Bank of Ireland, on behalf of Nama, to repay £48m of loans within 24 hours.
Those loans had originally been advanced to Kennedy Group companies by Bank of Ireland, AIB and Anglo Irish.
He said the group had sent annual business plans to Nama in October and November but the agency had been refusing to meet to discuss them.
In a statement, the administrators, from the Belfast-based accountancy and consultancy firm RSM McClure Watters, said that the hotel would remain open for business.
"We hope that people will continue to benefit from the hotel's facilities and our immediate objective is to maintain operations and honour bookings.
"Given the continuation of trade we look forward to working with the hotel's staff to drive the business forward."
DUP MP Gregory Campbell said the hotel was "quite crucial" to the causeway coast area.
"This is a well-run profitable establishment and the owners and many people in the community can't understand why Nama has moved to put it into administration," he said.
In October 2010, the construction arm of the Kennedy Group was placed into administration.
It consisted of J Kennedy and Co Contractors and three related firms, Kennedy Crane Hire, Kennedy Concrete Products and J Kennedy and Company (manufacturing).
A list of properties which have been repossessed by Nama included an industrial site on Letterloan Road in Coleraine. This is believed to be the former premises of Kennedy Concrete Products.
It is not clear why Nama has now decided to take further enforcement action against the group.
Mr Campbell and his fellow DUP MP Ian Paisley have expressed concern at the administration move and said they hoped to raise the matter with Nama through Finance Minister Sammy Wilson in the days ahead.
A leading north coast hotel has been put into administration by the Irish Republic's National Asset Management Agency (Nama).