American, United and Southwest have reported decreased demand for air travel as COVID-19 case counts and hospitalizations surged to record highs and sparked renewed lockdowns in some parts of the country.

“It’s really too soon to tell how deep and how long there may be a depressed environment but we’ve seen some weakening of bookings,” American president Robert Isom said at Thursday’s Skift Aviation Forum, according to CNBC.

United likewise warned of a “deceleration” in bookings and an increase in cancellations over the last week that it attributed to the spike in coronavirus infections. The Chicago-based carrier said it expects its scheduled flight capacity for the final three months of the year to shrink at least 55 percent from last year’s levels.

United “does not currently expect the recovery from COVID-19 to follow a linear path and, as such, the company’s actual flown capacity may differ materially from its currently scheduled capacity,” the airline said in a Thursday regulatory filing.

The comments came a week after Dallas-based Southwest said it had seen a slowdown in its “improving revenue trends,” though the company said it was unclear whether that was directly related to the coronavirus surge.

The warnings suggest airlines will face further pressure from the pandemic during the holiday travel season. The Centers for Disease Control and Prevention has urged Americans not to travel for Thanksgiving because of the US’s high infection rates.

While demand for air travel has recovered since the virus first struck this spring, passenger volumes for US airlines are still 63 percent below where they were a year ago despite carriers’ efforts to show that flights are safe, according to industry group Airlines for America.