By Juan Montes 

MEXICO CITY--Mexican President Enrique Peña Nieto submitted to Congress on Monday a telecommunications bill intended to boost competition in the quasimonopolistic markets dominated by tycoon Carlos Slim's América Móvil and broadcast company Grupo Televisa, just weeks after the country's telecom regulator imposed tough restrictions on both companies.

The proposed legislation is the final step toward overhauling rules governing the country's telecommunications and television markets, following constitutional changes passed last year in Congress.

Investors are awaiting the passage of so-called secondary laws to start taking decisions on new investments and corporate strategy, such as possible mergers and acquisitions.

Mr. Peña Nieto's proposals come at a decisive moment for Mexico's telecommunications market. In early March, the new telecom regulator declared América Móvil and Televisa dominant in their markets. As a result, the regulator ordered them to share infrastructure with competitors, banned them from obtaining exclusive rights to certain content such as sporting events, and imposed asymmetric interconnection tariffs on América Móvil.

The chances appear good for the bill to pass. The ruling Institutional Revolutionary Party, or PRI, along with two smaller allies, has almost enough votes in both houses of Congress to pass the bill, while the two main opposition parties have indicated they are willing to pass it during the current congressional period that runs through April.

Senators from the opposition, however, said that several changes to the bill will likely be made during negotiations.

The telecom bill gives unprecedented powers to the new regulator created last year--an autonomous body in charge of awarding concessions and determining dominant players.

The regulator will also function as a referee, settling disputes between incumbents and newcomers when they can't reach an agreement on rates to be paid for sharing infrastructure. It will also authorize the phone tariffs that dominant players, such as América Móvil, charge to the public.

The proposed law also raises fines for monopolistic practices. A firm could be fined as much as 4% of its previous year's revenue for trying to block the entrance of other competitors, compared with the current maximum fine of around $500,000.

Critically, the application of regulatory decisions can't be suspended while they are challenged in court. That is a huge advantage for regulators that in the past suffered endless litigation with companies that dragged measures through the courts as a way of avoiding regulation.

The changes could potentially attract new investors, including foreigners, to the mobile and TV markets, improving deficient services and lowering tariffs, many analysts say. Some say that the new rules will lead to mergers and acquisitions in the coming months that could transform the country's telecom market.

"The conditions are given to see the creation of two big players to compete face-to-face with Carlos Slim in the phone sector," said Ernesto Piedras, a telecom analyst with the consultancy firm the Competitive Intelligence Unit.

Mr. Piedras said that Spain's Telefónica can't afford to waste the opportunity to consolidate its position as the second-biggest mobile operator in Mexico, and that it will likely seek to merge with Iusacell, the third-largest mobile operator partially owned by Televisa, and other minor players such as Axtel or NII Holdings Inc. unit Nextel Mexico.

Telefónica officials have publicly left open the door to possible mergers or acquisitions in Mexico. Axtel and Nextel weren't immediately available for comment.

Some observers expressed skepticism about the bill, as it gives powers to the Interior Ministry to regulate TV advertising and content and to manage the related sanctions.

"This is a regressive step clearly intended to benefit Televisa," said Javier Corral, a senator with the conservative opposition National Action Party, or PAN. "They have taken from the telecom regulator an important tool."

America Movil's Slim controls around 80% of Mexico's fixed-line business and about 70% of mobile subscribers, while Televisa has around 70% of the TV market. Mexicans pay among the highest phone and broadband rates among member countries of the Organization for Economic Cooperation and Development.

In the television market, competition is expected to come with Mexico's first-ever tenders for two new digital broadcast networks.

A likely candidate to bid for one of the networks is Mr. Slim, who has shown great interest in the TV business in recent years and has the experience and the financial muscle to compete with Televisa. He could be allowed to bid if his companies comply with measures imposed on the phone market.

"If we get two more players [in television], we could see real competition in three or five years," said Jorge Negrete, head of consultancy Mediatelecom Policy & Law. "The new networks could be a game-changer for the advertising market, giving small and medium firms access to the advertising pie that is now monopolized by big corporations."

Although Mr. Slim's fixed-line company Telmex will be able to request authorization to offer television service, from which it is currently barred, there is no time for the company to obtain it before the network tender begins in June.

The bill proposed by Mr. Peña Nieto says the regulator will review compliance with the regulatory measures imposed on dominant companies such as Telmex in two years time, making it impossible for the company to get a single license for all telecommunications services in the short term.

If Mr. Slim decides to bid for a network concession, it is more likely he will apply through a different company in a joint venture with foreign partners, analysts and observers say.

A spokesman for Mr. Slim declined to comment on Mr. Slim's intentions to bid for a TV network until Mr. Peña Nieto's proposals are reviewed.

The telecom bill presented by Mr. Peña Nieto allows foreign investment of up to 49% in a broadcast TV station, which was previously forbidden.

Write to Juan Montes at juan.montes@wsj.com