Proposed European rules for pilots' flying hours and working conditions must be improved or safety could be at risk, MPs have warned.
A report by the House of Commons Transport Committee said night-time pilot duty proposals are a particular worry.
It is especially concerned at the "possibility that a pilot could land a plane after 22 hours awake".
The committee has examined draft proposals from the European Aviation Safety Agency (Easa) to change the rules that govern how many hours a pilot can fly.
It said airlines welcomed the suggestions but cabin crew and pilot representatives have expressed reservations, stating they "would have a negative impact on aviation safety in the UK".
Committee chairman Louise Ellman said the UK currently has stricter flight-time regulations than some other European countries, but under Easa's proposals it would not be able to have its own regime.
She said that under the existing UK rules "43% of pilots have reported falling asleep involuntarily at some point while on duty... and this shows how fatigue is already an issue in aviation".
The committee took evidence from consultant Mick Spencer, who has written his own report on the Easa proposals.
In its report, the committee said: "We share Mick Spencer's concern that 'the new regulations... could well lead to a situation where the accident risk will increase'."
Mrs Ellman said: "Current EU proposals risk making the situation worse, by lowering the UK's current standards. A lowest-common-denominator approach to safety will not benefit passengers, airlines or crew.
"The proposed 11-hour duty period at night for pilots flies in the face of scientific evidence. It should be reduced to a 10-hour maximum.
"We are also concerned at the possibility that a pilot could land a plane after 22 hours awake."
She added: "The Civil Aviation Authority (CAA) must do more to monitor pilot hours so that long duty periods are the exception not the rule.
"We are also concerned about a culture of under-reporting of pilot fatigue, which the CAA must tackle."
A Department for Transport spokeswoman said: "The safety of the travelling public is paramount, which is why we have been clear that we would only support Easa's final proposals if the CAA is content that they provide an appropriate level of protection against crew fatigue."
Jim McAuslan, general secretary of pilots' union Balpa , said: "This report should be a wake-up call to the Government that it must stand up for UK-level aviation safety standards and not allow them to be watered down.
"This is not for pilots' sake, but for the travelling public."