He said this moment was particularly crucial, as President Obama seeks to ease restrictions on doing business with Cuba and as more American companies flock there hoping to sign deals. Last week, the Obama administration approved the first American factory to operate in Cuba in more than 50 years, a small tractor company from Alabama.

The Helms-Burton Act, signed by President Bill Clinton in 1996, says that anyone who profits from properties that were confiscated from American citizens is liable for damages, even if the owner was not an American citizen at the time. Yet the law has provisos that allow the president to decide whether, for the sake of American interests, the law should be enforced.

It has pretty much never been enforced.

“It would be a slug fest,” said Pedro A. Freyre, a Miami lawyer who specializes in Cuban business deals. “It would be a brawl, a free-for-all, everyone suing every Canadian company, airline, hotel, you name it — and it would be detrimental to U.S. foreign relations.”

Martha Pantin, a spokeswoman for American Airlines, which is expected to bid for the Cuba routes, said Mr. López’s problem is one best answered by government agencies. “This is not an airline issue,” she said.

A State Department spokesman, who spoke on the condition of anonymity in keeping with department policy, said officials in the United States and their Cuban counterparts had touched on the topic during aviation talks. The department is negotiating with the Cubans over compensation for confiscated properties, but the cases of people who were not American citizens at the time of the confiscations were not included in those talks.

And unlike after the fall of the Berlin Wall, when heirs of property owners in the former East Germany received compensation for seized assets, the confiscators in Cuba are still in power.