"We will take steps to try and ensure your safety, as we do not trust the Provos (our Black September group)."
The letter added that it was unlikely that any of the All Blacks team would be treated as hostile visitors, although "they play a foreign game and have close Ulster associations".
"No such immunity can be extended to any British team," it continues. "So we can assure you that it was with good reason that the Scots and Welsh teams did not come here.
"By way of advice, we suggest that you should refrain from talking about politics.
"You should also refrain from making any comment on communication. If you do, apart from other measures, we will follow our usual practice of denying all knowledge or responsibility."
Burgess passed the letter onto the publishers of the book, Mower Books. It is not known why the letter was sent to Burgess, a first five-eighth, as opposed to directly to New Zealand Rugby. But Burgess was seen as one the more academic players in the 1973 squad and was also known to have strong views.
The All Blacks tour occurred during the height of the "Troubles" between Catholic and Protestant communities in Ulster.
Burgess told the book's authors he received the letter after the All Blacks had played in Belfast against Ulster on November 18, ahead of the planned test against Ireland in Dublin on January 20.
"I recall being nervous about going to Ulster during the Troubles but it wasn't really discussed," Burgess said. "The NZRU had agreed to a tour and that was on the agenda, so everybody knew the game was on.
"What we didn't appreciate was what was illustrated in the letter I received before the Irish Test. And that was the level of antagonism by many people in Ireland to the English, Scots and Welsh rugby teams.
"It was something that was discussed but only in a minor way because I don't think we really appreciated the politics of what we were getting into."
Burgess said the All Blacks stayed in a hotel just north of Belfast.
"We drove by bus to the game by what I understand was a rather circuitous route taking half an hour longer than we might have expected to take and I'm sure that was to do with secrecy.
"When we got to the ground, and right through the game, on the top of the stadium, which was like an amphitheatre, there were armed soldiers. We saw them at training on the Thursday before the game. We trained at Ballymena, north of Belfast, and it was snowing. God it was cold, snow on the ground and these British military forces were there all armed with machine-guns which they happily showed us.
"The reception we got on the day of the game was huge. When we ran onto the ground there was such a roar and hand clapping that just carried on and on and on, and the same at the end of the game. I think we knew that our presence had been appreciated.
"There was an uneasy feeling that what we were doing was political and that we were being used other than for it just being a game of football. The four Home Unions were wanting to make a point. England played in Dublin in 1973, but it was 1974 before Wales and Scotland went there, and neither team played Ireland at all in 1972."
Burgess said he was not aware of any other players receiving the letter.
"I didn't turn it into a point of discussion with the other players and I'm not aware of who the other players might have been who could well have received it," he said.
"I do think I may have received it because my stance against South Africa was well known. That stance wasn't a topic that was brought up at all by other players during the tour and I didn't bring it up as an issue. It was simply something in the background as everyone was aware of my stance. They may have commented among themselves but not with me. There were others including Bruce Robertson and Sandy McNichol, who were opposed to the Springboks coming in 1973, but that was after the team came back to New Zealand.
During the test in Dublin, which ended in a 10-all daw with Irish fullback Barry McGann missing a conversion to win the game, there was an explosion downtown which Burgess said that was audible at the ground.
"I don't think it registered with any of the All Blacks but it certainly did with the Irish team and I think it affected their playing somewhat. It could have rattled them. I have often wondered if McGann, in attempting the conversion, was put off by a bomb?"
