Shares of America Movil (AMX) - Get Report are falling by 4.7% to $12.77 on Thursday afternoon, after regulators in Mexico increased the antitrust rules against billionaire Carlos Slim's telecom company, Reuters reports.

America Movil has 65 working days to submit a plan that will separate part of its fixed line unit Telmex. The The Federal Telecommunications Institute has increased antitrust rules against the company in order to leave further room for competition in the space. 

(This story was updated from 10:20 a.m. to include further antitrust details.)