Mexican telecoms regulator IFT said on Sunday that it will force Telmex to offer competitors better terms as it seeks to open up its local network, part of an effort to increase competition in a sector dominated by billionaire Carlos Slim.
The move will require Telmex, owned by Slim's América Móvil, to modify the terms and conditions under which it will let other companies use part of its vast fixed line infrastructure.
The so-called "last mile" connects competitors using Telmex's fixed line infrastructure with their end-user customers.
Once Telmex is formally notified of the decision, the company has 20 days to present a new plan, the Federal Telecommunications Institute (IFT) said in a statement.
Since declaring América Móvil dominant last year, the IFT has been introducing stricter measures designed to boost access to a sector seen as less competitive than Mexico's peers.
América Móvil operates around 70 percent of Mexico's mobile and fixed lines.