SoRCon 8 27 Feb - 1 Mar 2015 Basildon UK http://www.sorcon.co.uk Essex Games 27 Jul '15
We can't find this clearly in the rules. It seems like the player that fills the auction track must also call Ra.
Just consider how the game plays. Each turn you draw a tile or call Ra. Player draws a tile. He's done his thing. He doesn't get to do two things. Calling Ra would be doing two things. So on to the next player. Draw a tile or call Ra. But the first isn't available. So call Ra.
(There's a special exemption in this case that the call isn't voluntary.)