IF YOU have ever clicked on an internet advertisement for a super-low airfare and found, to your surprise, that the actual price was much higher, Barack Obama's Department of Transportation has good news. Starting in late January, the Obama administration will crack down on airlines that don't show the total price, including taxes and fees, of the flights they're advertising.

Not all the airlines are thrilled about this, as the New York Times's Susan Stellin explained in a helpful article last week. Three low-cost airlines—Spirit, Allegiant and the market-leading Southwest—have sued the government, saying the regulation infringes on their free-speech rights. Ms Stellin illuminated exactly why Spirit, at least, is so peeved:

Spirit has built its business around advertising $9 fares, then charging additional fees for checked and carry-on bags, advance seat assignments and now a “passenger usage fee” of up to $17 each way for tickets booked online. Since that online booking fee is technically optional — travelers can instead drive to the airport and buy a ticket there — Spirit is not required to include it in advertised prices. The proliferation of these types of fees has prompted the government to impose a growing number of fines against airlines and travel agencies that violate existing rules.

This is exactly the sort of advertising that governments should be able to prevent. Almost no one actually travels to an airport to purchase an airline ticket, and Spirit's barely even trying to hide the fact that the "passenger usage fee" is essentially part of the fare. What is the passenger "using" if not the flight? Surely the $17 (each way!) is more than enough to cover Spirit's server and technology costs for an internet booking—in fact, it's hard to imagine that the passengers who actually do go to the airport to book their fares don't cost the airline more per customer than the internet bookings.

It's a shame that airlines won't disclose the full costs of their products, including taxes, without prodding from the government. Ideally, this kind of regulation wouldn't be necessary at all—and airlines that opposed high taxes on their flights would simply err on the side of giving their customers more information, not less. There are better ways to make your customers aware of the costs of government than trying to make taxes and fees disappear from your ads. (There's also the issue of confusing your customers about which costs are taxes and which are fees. Will a customer necessarily realise that the "passenger usage fee" is Spirit's and not the government's?)

In any case, Spirit et al are likely to lose their court fight. "The Supreme Court has said in the context of commercial advertising, the government has a very broad right to mandate speech that is reasonably aimed at preventing people from being misled," Eugene Volokh, a law professor at the University of California, Los Angeles (and prominent legal blogger), told the Times. "[M]ost likely [the new rule] will be upheld."