(Telecompaper) Free Mobile has written to rivals Bouygues Telecom and SFR and asked to join their proposed network-sharing venture. Free also wrote to the competition regulator and telecoms regulator Arcep about the proposal, Les Echos reports. An agreement between two of the three original operators that was not open to the fourth operator would be a "major destabilisation factor" in the market, according to the letter from Maxime Lombardini, the CEO of Free's parent company Iliad. The CEO called on the two operators to make a proposal to include Free in the RAN sharing agreement. SFR said Free's request was premature given it's still in talks with Bouygues about the technical and legal structure of the agreement. The companies said previously that they aimed to reach an agreement before the end of this year, but the talks are running one or two months behind schedule, SFR said. They also will need to consult their works councils before finalising the deal. Bouygues Telecom declined to comment on Free's proposal.