The first direct maritime shipment from Miami to Cuba in more than 50 years is scheduled to depart from a Miami River terminal Wednesday morning.

It’s the start of weekly service by International Port Corp., a Miami River terminal operator, that will ferry humanitarian items to Cuba that are permissible under exclusions to the U.S. trade embargo.

“We are not shipping anything that is commercial or that will be resold,’’ said Leonardo Sanchez-Adega, a spokesman for International Port Corp.

Its customers are religious groups, non-governmental organizations and charitable groups that are legally authorized to send humanitarian shipments to Cuba as well as individuals shipping packages to family and friends in Cuba.

The company’s delivery service is licensed by both the Office of Foreign Assets Control and the U.S. Commerce Dept., said Sanchez-Adega.

International Port’s first Cuba-bound ship, the leased Ana Cecilia, is scheduled to leave the Miami River at 11 a.m. Wednesday. The largest items it will be carrying on its first voyage are mattresses and it will return to Miami empty.

The Ana Cecilia is scheduled to arrive in Havana at 7 a.m. Thursday. There recipients will have the option of picking up their shipments at the port or using CubaPACK, which promises to deliver to the Havana area within a week and to locations throughout the island within two weeks.

CubaPACK is a package delivery company set up by the Cuban government to handle humanitarian shipments.

International Port Corp. will charge $5.99 per pound, including delivery, for its shipments.

Shipping via sea is an alternative to third-country shipments and ferrying large packages of food, clothing, and other items on air charters. In recent years Cuban exiles have shipped everything from building supplies to bicycles and large televisions via air.

“It’s really become a little untenable at the airport,’’ said Sanchez-Adega. “This is a way to send shipments quickly, efficiently and legally.’’

South Florida Republican Rep. Ileana Ros-Lehtinen sent a letter to Adam Szubin, director of OFAC, on June 19, asking if International Port Corp. was in violation of any U.S. laws or regulations. Her office distributed the letter to the media Tuesday.

In her letter, Ros-Lehtinen highlighted a provision of the Helms-Burton law that “states no vessel that enters Cuba to engage in trade of goods may enter a U.S. port for the purpose of loading or unloading freight for a period of 180 days from the date the vessel departed Cuba.’’ That provision generally applies to ships that visit Cuba without U.S. permission.

“That’s OK. That’s her job. We would have given her a full response but we haven’t heard from her,’’ said Sanchez-Adega. “This seems to me to be a little bit of theater. We’ve done this above board and we’ve been working on this for quite some time.’’

Alex Cruz, Ros-Lehtinen’s spokesman, said Tuesday that she hadn’t received a response from OFAC.

International Port Corp. isn’t the first Florida company to offer direct delivery of humanitarian shipments to Cuba, but it will be the first in many decades to offer regular weekly service from Miami, said Sanchez-Adega.

Crowley Maritime already has regularly scheduled service to Havana from Port Everglades every Monday under an OFAC license to carry humanitarian and agricultural products and it has transported everything from frozen chicken to live cattle.

After a change in U.S. regulations during the Clinton administration that allowed the transport of agricultural commodities, medicine, medical devices or other products directly from the United States to Cuba, Crowley became the first U.S. shipping line to re-enter Cuba in nearly 40 years in December 2001. It has had regularly scheduled service ever since.