* Bill to increase competition could take effect in 2014
* Asymmetric rates would be imposed on dominant players
* Spending on share buyback nearly tripled so far this year
MEXICO CITY, April 30 (Reuters) - New legislation in Mexico could materially affect the business of America Movil, Latin America's largest telecommunications company, the company controlled by billionaire Carlos Slim said in a U.S. regulatory filing on Tuesday.
Mexico's Senate on Tuesday was expected to approve a bill designed to increase competition in the country's phone and television markets, dominated by America Movil and Emilio Azcarraga Televisa.
The legislation would impose certain measures including asymmetric rates on dominant players including America Movil, which has around 70 percent of the mobile market and 80 percent of the fixed-line market in Mexico.
Once the bill is approved by the Senate, it must be approved by legislatures in the majority of Mexico's states. Mexico's Congress will also need to draw up secondary legislation to implement the new rules.
"We expect that the bill will become effective in substantially its current form," said America Movil in the filing. "If it is approved rapidly, we would expect specific rules and regulations to begin taking effect in 2014."
America Movil shares have tumbled more than 14 percent since the start of the year, hurt by the threat of increased regulation as a result of the reform, as well as weak results.
On a call with analysts earlier this month, executives said the company would not make any strategic changes until it knows the details of the secondary laws to follow.
The company has been buying back shares to try and support its share price.
America Movil has spent 22.8 billion pesos ($1.88 billion)buying back more than 1.8 billion shares in the year through Monday, almost three times the 8.4 billion pesos it spent buying back just under 550 million shares in the first four months of 2012, the filing showed.