Foreign investment is permitted up to a total of 49% of equity in interior navigation and coastal sailing (other than tourist cruises and  the exploitation of dredges and other naval devices for ports), integral port administration and port pilot services for interior navigation. Full ownership may be authorised in foreign commerce shipping and port services pertaining to interior navigation subject to the approval of the National Foreign Investment Commission.
"ARTICLE 2.- For the purposes of this Law, it shall be understood as: [...]
II.- Foreign investment:
a) The participation of foreign investors, in any proportion, in the capital stock of Mexican companies;
b) That carried out by Mexican companies with a majority of foreign capital; and
c) The participation of foreign investors in the activities and acts contemplated by this Law.
III.- Foreign investor: to the natural or legal person of a nationality other than Mexican and foreign entities without legal personality;
[...]
ARTICLE 3.- For the purposes of this Law, that made by foreigners in the country with the condition of Permanent Resident stay is equated to Mexican investment, except for that carried out in the activities contemplated in Titles One and Two of this Law.
ARTICLE 4.- Foreign investment may participate in any proportion in the capital stock of Mexican companies, acquire fixed assets, enter new fields of economic activity or manufacture new product lines, open and operate establishments, and expand or relocate existing ones, except for the provisions of this Law.
The rules on the participation of foreign investment in the activities of the financial sector contemplated in this Law shall be applied without prejudice to what is established in the specific laws for those activities.
For purposes of determining the percentage of foreign investment in economic activities subject to maximum participation limits, foreign indirect investment will not be counted, is carried out in such activities through Mexican companies with a majority of Mexican capital, provided that the latter are not controlled by foreign investment.
[...]
ARTICLE 7.- In the economic activities and companies mentioned below, foreign investment may participate in the following percentages: [...]
III.- Up to 49% in: [...]
t) Comprehensive port administration;
u) Port services for piloting vessels to carry out inland navigation operations under the terms of the Law on the matter;
v) Shipping companies dedicated to the commercial exploitation of vessels for inland navigation and cabotage, with the exception of tourist cruises and the exploitation of dredgers and naval devices for the construction, conservation and port operation; [...]
The limits for the participation of foreign investment indicated in this article may not be exceeded directly, or through trusts, agreements, social or statutory agreements, schemes of pyramiding, or any other mechanism that grants control or a participation greater than that established, except for the provisions of Title Five of this Law.
ARTICLE 8.- A favorable resolution of the Commission is required for foreign investment to participate in a percentage greater than 49% in the economic activities and companies mentioned below:
I.- Port services to vessels to carry out their inland navigation operations, such as towing, rope mooring and launching;
II.- Shipping companies dedicated to the exploitation of vessels exclusively in high-altitude traffic; [...]" (Foreign Investment Law (27 December 1993), last amended on 15 June 2018, Articles 2, 3, 4, 7 and 8 [google translation])
Foreign Investment Law (27 December 1993), last amended on 15 June 2018, Articles 2, 3, 4, 7 and 8
[<a href="http://www.diputados.gob.mx/LeyesBiblio/pdf/44_150618.pdf">Law</a>]