Let’s talk about taxes. Wait a second, come back here! I mean airfare taxes.

The subject comes up because of what Congress just did — or, rather, did not do — and what the airlines did in response.

On Friday, Congress failed to approve the extension of a bill to keep the Federal Aviation Administration running. Among other things, that meant the agency no longer had the authority to impose the various federal taxes that airlines add to the price of each ticket.

So as of 12:01 a.m. Saturday, the federal government began losing an estimated $25 million a day in tax revenue.

But did airlines simply pass on this savings to customers?

No, they did not.

Last week, evidently in anticipation of the tax’s expiring, some airlines quietly began raising fares — on average, roughly by the same amount as the federal taxes. Others did the same over the weekend, and most of the rest joined in on Monday.