Yes! The scene is riffing on actual occurrences that would have been familiar to viewers at the time the movie was released (1980) but are practically unheard of today. During the 1970s-80s, religious and political solicitors were commonly encountered in airport terminals: Hare Kirshnas, Moonies, Jews for Jesus, advocates of various political causes, etc. They would hand out flowers and pamphlets, talk about their beliefs, and very frequently ask for money on the spot. The stereotypical Hare Krishna approach was to offer a flower and begin telling a personal conversion story, then ask for money when the traveler tried to go. To cut through the awkwardness, some travelers would make small donations.

Judging by newspaper accounts, this was extremely unpopular with travelers, many of whom felt trapped, worried about missing connections, and otherwise resented the experience.

Indeed, I think moviegoers were expected to identify with Robert Stack and wish we could punch the solicitors' lights out. (Of course, a lot of it's just funny: there's a scene a bit earlier where a member of the Church of Religious Consciousness solicits two Hare Krishnas who happen to be in the airport to travel, so they blow her off. Those two passengers end up on the Aiplane! itself. So the overall gag is that Hare Krishnas must find travel tedious, too.)

Airport authorities attempted to limit such solicitations but ran afoul of the public forum doctrine that had been set forth by the U.S. Supreme Court in the 1939 case Hague v. Committee for Industrial Organization and developed in subsequent cases. Under that doctrine, citizens had the right to use public spaces such as streets and parks--the traditional "public square," in other words--to meet, discuss, and distribute literature on questions of public importance. Limitations had to be narrowly tailored and advance a compelling state interest. Nearly all courts analogized airport terminals to public squares and considered them traditional public fora, so they tended to strike down any limitations. Some airport authorities did work out enforceable limits (or compromises) under which the solicitors were restricted to certain parts of the terminal.

In 1988, the Port Authority of New York and New Jersey (which manages JFK, La Guardia, and Newark airports) enacted broad restrictions on airport solicitations that, if upheld, would basically shut down solicitations by banning solicitation of funds and distribution of literature at all times in the airport. The Hare Krishna organization (properly, the International Society for Krishna Consciousness, Inc.) sued to keep the regulation from going into effect. As usual, the trial court struck down the ban. The Court of Appeals, however, held that the airport terminal was not a public forum at all and said that the ban on soliciting donations was permissible (though the ban on distributing literature was not).

The case then went to the U.S. Supreme Court, where it was known as International Society for Krishna Consciousness v. Lee. The Court's 1992 decision affirmed the Court of Appeals by a 6-3 split and held that the airport terminal was not a public forum. Chief Justice Rehnquist, writing for the majority, explained that airport terminals were not traditional public fora. They were too new and thus were not like public squares or streets where such activity had long been allowed. Rather, they were focused on transportation. So restrictions on solicitation would be upheld as long as they were reasonable. The Port Authority's ban was reasonable since it addressed the congestion, duress, and fraud that resulted from solicitation. Although Rehnquist would have also upheld the ban on distributing literature, the three dissenters from the main opinion and two other justices disagreed, so distribution of literature was still allowed.

At the time of the decision, the Washington Post described airport solicitations as "ubiquitous."

After the case was decided, many airports enacted similar bans, so in the 1990s, solicitors gradually disappeared from most airport terminals. The increase in airport security and efficiency after 9/11 played a role as well, at which point the 20-year rule applies. But if your memories of air travel don't extend past the mid-90s, then it's entirely possible you never encountered airport solicitors, whereas you quite likely would have in the previous few decades.