In an internal memo obtained Friday by The Associated Press, Delta Air Lines said gate agents can offer up to $2,000, up from a previous maximum of $800, and supervisors can offer up to $9,950 (£7,943), up from $1,350.

United is reviewing its own policies, including incentives for customers, and will announce any actions by April 30, a spokeswoman said. The airline would not disclose its current compensation limit.

Last year Delta got more passengers to give up their seats than any other U.S. airline, partly by paying more than most of the others.

Delta no doubt hopes that gate agents and their supervisors won't need to make maximum offers, and the financial cost to the airline is likely to be limited. If Delta paid $9,950 to every person it bumped involuntarily last year, that would total $12 million. Delta earned nearly $4.4 billion.

An Associated Press analysis of government data shows that in 2015 and 2016, Delta paid an average of $1,118 in compensation for every passenger that it denied a seat. Southwest Airlines paid $758, United $565, and American Airlines $554.