Te Tii Marae committee chairman Hama Apiata said yesterday if media refused to pay they would not be allowed on to the lower marae at Waitangi this weekend.
Only one organisation - the local Maori radio station - would be exempt from the fee, he said.
NZPA reported Ngapuhi leader David Rankin yesterday saying the move was apartheid.
Mr Key this morning said he wanted to know what the fee was for.
"If it's cost recovery that might be reasonable but charging the media for a fee for covering our national day of celebration in my view seems unreasonable.
"I think we need to find out exactly what the fee is being paid for. I guess we'll make some inquiries. Whether we get straight answers is a completely different issue. I mean it's fundamentally not public space, but I think it's really the message that it sends."
The move felt "like it's a money-making exercise".
Some public funding went to the marae, but Mr Key did not know how much.
"It's happened before, it's not new, but it is, as I say, very disappointing. I mean we want the media to be able to cover the celebrations at the lower marae, because we want New Zealanders to be able to see and understand and enjoy the significance of Waitangi Day."
Last year, several media groups were charged $500 to enter and report on the day's festivities at Te Tii Marae, which is across the river from the main Waitangi Treaty Grounds. Some rejected the fee demand and negotiated entry by paying a koha of up to $40.
Mr Rankin said there was no record of where the money went.
"This is not a koha, it is deemed as income because it is demanded from people. It goes completely against our culture of hospitality to visitors, regardless of where they are from."
He said the fee amounted to "cultural apartheid" and he would be advising all media that the marae was open and free of charge this Waitangi Day.
"Many of our people outside of Northland will be depending on the nightly news for information about Waitangi Day, and this small, unelected group are threatening to ban media coverage for the sake of their own personal greed."
Media Freedom Committee secretary and NZPA chief executive Tim Pankhurst said it was disappointing the issue had risen again and it threatened to take the spotlight away from what actually happened on the lower marae.
"It's extortion. It's not koha, media have a right to report fairly on matters of national importance and surely, the commemoration of our national day."
He urged media to resist paying the fee and reporters should instead go on to the marae with the official party.
"It's not going to look great if they are walking on with the prime minister and they are barred from entry. In that case I would think he should have something to say."
Mr Apiata said that because things "got messy" in the past, it had been tidied up, Newstalk ZB reported.
Everyone paid equally, he said.
Television stations had already paid the fee so it was likely other media would follow, the station reported.
