The players signed are Manawatu lock Hayden Triggs, Manawatu midfield back Johnny Leota, Hawkes Bay prop Clint Newland and Taranaki inside back Jayden Hayward.
Triggs, Leota and Newland all played for the Highlanders this year, while Hayward has had a stand-out year for Taranaki.
ORFU chief executive Richard Reid said securing the players was not a way to get around the rules and other franchises were doing it.
Canterbury announced yesterday it had signed Bronson Murray and Jared Payne from Northland, and Thomas Waldrom from Wellington.
The two Northland players will return to the Taniwhas next year, while Waldrom will play for Hawkes Bay.
The Blues also signed Tasesa Lavea last week but he will play next year for Chiefs franchise union Counties-Manukau next year.
Reid said the way the transfer-loan system worked was that players could make judgement calls in where they wanted to play Super 14 rugby.
With flying winger Fetu'u Vainikolo signed by the Otago union for a permanent move south next year, yesterday's announcement brings more continuity to the Highlanders squad.
The franchise had presented a paper to the New Zealand Rugby Union board in August asking to be allowed to hold on to its eight draft players for next year to bring some continuity to the side, but it was turned down by the board.
"We've always argued that you can't build a team in one year," Reid said.
"Some continuity is essential and this arrangement provides that. Securing someone with the talent of Hayward is a bonus."
Reid said the players could not play for Otago next year as they still had outstanding contracts with provincial unions for the Air New Zealand Cup in 2009.
Highlanders coach Glenn Moore said the objective was always to get some continuity into the side, and the signing of Triggs, Leota and Newland helped that.
"The guys were very keen to come back. They all performed well for us last season and enjoyed the campaign and team spirit," Moore said.
Moore said Hayward was a very promising player, who had good vision and good management of space.
Hayward, who turns 21 next month, has impressed in his first year at first-class level, and was one of the catalysts in getting Taranaki into the Air New Zealand Cup quarterfinals.
He can play first five-eighth and second five-eighth and can also kick goals.
The Highlanders drafted eight players last season and, with yesterday's signings, have secured four of them to play next year.
Counties-Manukau centre Niva Ta'auso is leaving to play in Ireland, while Canterbury fullback Paul Williams is believed to be heading for the Blues.
Canterbury lock Isaac Ross and Bay of Plenty first five-eighth Mike Delany may not come back to the franchise as there are players in the Highlanders region to replace them.
Southland lock Josh Bekhuis looks an obvious candidate to replace Ross while Blair Stewart, Chris Noakes and Robbie Robinson look like options for the No 10 jersey to replace Delany.
Moore said it had been frustrating to watch Otago's season, and it was always better to have franchise teams right up there in the competition.
Otago finished 10th in the Air New Zealand Cup while Southland was fifth.
The 28-strong Highlanders squad is due to be named at the end of the month, although the draw for next season has yet to be finalised.
The move to expand the play-offs to six teams has caused a change in the draw, and is still being worked through.
