The regions did not oppose central contracts entirely, but said they needed to be part of a "collective agreement between all four regions".
RRW have been asked to respond to Warburton's comments while the Blues said they had nothing to add to Wednesday evening's RRW statement.
a statement on Thursday afternoon,
the WRU said it encouraged the regions to contract as many key players as they could, but if they were unable to sign them, the WRU would be prepared to negotiate central contracts with players to keep them in Wales - as it did with Warburton.
In his newspaper column, Warburton wrote: "I hope nobody thinks that I am turning my back on the Blues. I am not. I supported Cardiff as a youngster and have come through their system.
"I am Cardiff through and through and would find it uncomfortable playing for anyone else. If I had not been able to play for the Blues, it would have been back to the drawing board."
Warburton was one of six leading Wales players coming to the end of their regional contracts who were understood to have been offered deals by the WRU.
"I thought it was a great opportunity for me to sign with the union," writes Warburton.
"For me it is a win/win situation. I can train with the Blues and play for them. In that respect everything will be as it is now."
Warburton says he has been given no guarantees when it comes to Wales selection but does believe central contracts can work as they do in Ireland and New Zealand.
"I am sure more Wales players will sign up, and it will become clear that it is not the WRU competing against the regions. It is about everyone working together," he writes.
"I know that there is still so much uncertainty about the game in Wales, with the WRU and the four regions not having come to an agreement, and a deadline having been set by the regions for that to happen by tomorrow (Friday).
"But that is where I have a lot of faith that things will work out."
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