Beginning Jan. 1, it will be easier to prosecute airline passengers who start fights, are verbally abusive abuse or smoke on board planes, under a new international treaty.

A loophole in rules set in 1963 means that jurisdiction over what the airline industry terms “unruly” passengers lies in the country where the aircraft is registered. But when a plane lands thousands of miles from home, that can mean the offending passenger is handed over to authorities who are essentially powerless.

“Everybody on board is entitled to enjoy a journey free from abusive or other unacceptable behavior,” said Alexandre de Juniac, head of the International Air Transport Association, a trade group. “But the deterrent to unruly behavior is weak.”

Juniac said in a statement that six in 10 offenses go unpunished.

But the rules are set to change after Nigeria ratified the new treaty last week, giving it the required support from 22 nations. De Juniac said the change will strengthen the deterrent.

The treaty, properly known as the Protocol to Amend the Convention on Offences and Certain Other Acts Committed on Board Aircraft, done at Montreal on April 4, 2014, is overseen by the U.N. aviation agency ICAO. The organization’s director, Fang Liu, said the change “addresses the issue of rising incidents of unruly and disruptive behavior.”

Under current treaty rules, if an international flight has to turn around and remains in its home country, passengers can be held to account. In February, for example, a British man who was heavily drunk on a flight from Calgary to London was convicted and ordered to pay for 20,000 pounds of fuel the pilot had to dump to land safely back in Calgary.

But in other cases, for example where a plane is diverted to a third country or continues to its original overseas destination, little can be done. And planes are often leased, meaning their flights might never involve the country where they’re registered.

According to data IATA collected from its members, which account for the vast majority of global passenger traffic, the problem has been steadily getting worse.

There was an incident of unruliness on 1 out of every 1,053 flights in 2017, according to IATA. That was up from 1 in 1,424 flights in 2016.

About a quarter of cases involved passengers who were drunk or on drugs, and another quarter involved people smoking, IATA says. The vast majority of incidents are minor, but IATA says 4% involved behavior it defines as the most serious, like a passenger trying to get into the cockpit.

Airlines have been beefing up crew training for dealing with belligerent travelers and have options short of criminal prosecution for dealing with people whose behavior creates a safety problem.

That can include issuing six-figure bills, as the British airline Jet2 did this summer when it charged a woman who tried to open a door midflight $106,000.

In the United States, unruly passengers can face criminal prosecution or fines up to $25,000 from the Federal Aviation Administration. The agency pursued 120 cases in 2018.