Gordon Brown has been accused of overruling his officials to make sure a new air tax covers families who have already booked spring half-term breaks.
Mr Brown defended the timing of the tax
The Conservatives say the chancellor ignored advice to bring in the extra £5 air tax in April, instead deciding on a February start, raising an extra £100m.
The chancellor told a committee of MPs he had consulted Treasury officials, but it was his decision to make.
He said it would be wrong for people to draw the conclusion he overruled them.
Giving evidence to the Treasury Select Committee, Mr Brown pointed out that fuel duty changes for cars were brought in immediately, and that the industry had been given a period of three months to adjust to the new rate.
When asked by Tory MP Brooks Newmark whether he had overruled his officials who, according to newspaper reports, had advised him to bring the new rate in April, the chancellor said: "I don't think that is the case."
Mr Newmark replied: "You don't think it is... or it is the case?"
Mr Brown said: "I think you'll find decisions in the Treasury are made by the chancellor after taking advice from his officials."
However, he then added that all decisions were made by himself as the chancellor.
He said it was not a cast-iron rule that tax changes had to happen in April, at the end of the financial year.
British Airways had told the committee it needed more time to phase in the changes.
It said: "Hundreds and thousands of passengers have already booked and paid for travel at the present APD rate for travel that's going to take place after 1 February."
It would cost BA £6m to make up the shortfall and the industry as a whole £100m.
Mr Brown suggested the airlines surcharge passengers in the same way they did when fuel prices went up.
"When the airlines charge surcharges for fuel they charge it on existing tickets as well as new tickets and holiday operators have often done that as well.
"I think that the whole issue of the air passenger duty tax has got to be seen in the context that this is a departures tax. It's not bookings tax, it is not a tickets tax, it is a departure tax.
"And actually, if a passenger doesn't turn up and has paid the departure tax, the airlines get it back."
He said there have been "discussions between ourselves and the industry and these continue".
Asked if he had the authority to make airlines pay the tax before the change had been authorised by the Commons, he said: "I believe we do."