A U.S. law first enacted in the 1990s allowing Americans to sue corporations doing business in Cuba is finally being allowed to take effect.

Signed by President Bill Clinton, the Libertad Act, also known as the Helms-Burton Act, was intended to strengthen the U.S. embargo on Cuba. But a waiver was granted for a section known as Title III, which allowed U.S. courts to hold companies doing business in or with Cuba liable for damages to U.S. citizens harmed by the Castro regime.

Every President since Clinton continued to waive that section of the act, but just this year, President Trump announced it will now be in effect. Now, two men with ties to seized seaports in Cuba are the first to file lawsuits, doing so in the U.S. Court for the Southern District of Florida. Their target: Florida-based Carnival Corporation, which operates of a number of cruise lines bringing vacationers to Cuba via those ports.

"The original sin of the Cuban Revolution, among other things, was the theft of all property in Cuba,' says Javier Garcia-Behgochea. "Literally everything in Cuba is stolen."

Garcia-Behgochea's family, he claims, is the rightful owner of the seaport in Santiago de Cuba, the island's second largest city. The family raised the capital in 1920 to build and operate the docks, exporting agricultural products.

But after Fidel Castro's rise in 1959, Garcia-Behgochea and his family watched as the guerrillas now in charge started confiscating whatever they could. Castro was nationalizing production of goods and converting Cuba to a centrally planned economy. First, the regime seized property and businesses owned by U.S. or other foreign nationals. What happened next was "unthinkable," recalls Garcia-Behgochea.  He claims men sent by Castro, scraggily bearded and dressed in military fatigues, stormed the offices of 386 private Cuban businesses, forcing out the owners. And once they were out, these owning families often felt endangered.  "Cubans were disturbed by the confiscation of foreign national's property," he says.  "Our first concern was the Cubans wouldn't tolerate this and there would be civil war, and so we left Cuba."

The seaports will now be the first test of how viable lawsuits filed under the Libertad Act will be. A second plaintiff has a photograph, taken by his grandmother, of the day Castro's men showed up at his grandfather's office at Havana Docks Corporation. Like Garcia-Behgochea's family in the other city, Behn's Cuban-American family built the seaport in the capital of Havana, and when Castro came to power, they used the port to help Cubans targeted by the Revolution flee to safety. But after the business was taken, the Behn family would also escape to Florida. "My mother was only five years old when they left and never returned back,” Behn says. "I was brought up in Miami only because of the Cuba situation."

Castro would later claim Havana Docks was nationalized because the Behn family had abandoned it, and the police found the offices empty following the family's flight. But Behn claims his grandmother's photograph proves the Castro regime was lying.

The fight in court between the men and Carnival will not likely end with either family regaining their property. But their goal, they say, is justice in whatever form they can get. Their attorney, Bob Martinez of Miami law firm Colson Hicks Eidson, says justice for Behn and Garcia-Behgochea will also mean justice might come one day sooner for the Cuban people.

"Those properties right now are run by the Castro regime," says Martinez, himself a Cuban exile. "To say the people benefit because tourists get offloaded, or a tourist may throw some dimes here or there, or some gratuities to the Cuban people, is a joke."

And both men feel Carnival is just as guilty.

"Carnival is trafficking in our stolen property in violation of the law, and we thank God we have this venue in this great country to address that grievance," adds Garcia-Behgochea. It's why the men have kept their respective families' corporations active, all these years later. Behn claims Carnival began sailing into Havana shortly after his grandfather died. "My grandfather spoke about his love for Cuba, his love for his business in Cuba. How life was beautiful and all he ever wanted was to go back, and which is why we kept the company alive.  Our company is still operating since 1917, until today, specifically to get back our ports.”  Behn surmises, “The cruise lines have ignored us."

Carnival will soon need to respond in court to the men’s claims. So far, the company declines to comment on the matter. But a Carnival spokesperson would quote to FOX News an earlier statement made by the Cruise Line Industry Association: "Cruising to Cuba falls under the lawful travel exemption under Title III of the Helms-Burton Act. Our cruise members have been and are now engaged in lawful travel to Cuba as expressly authorized by U.S. federal government."

Eben Brown is a FOX News National Correspondent based in Miami.  Follow him on Twitter: @FOXEbenBrown