About 1.5 million public workers have been affected by the change which took effect on Tuesday.

They had been able to take two or three hours off in the afternoon - for a big meal or a second job - then work until 9pm or 10pm.

Office staff run up electricity costs at night

It is hoped the plan, which was put forward by the Treasury Secretariat and the Federal Comptroller's Office, will save almost $200m by cutting down on electricity costs in the evening.

The move has been welcomed in some quarters. Analyst Sergio Sarmiento said: "Mexican work schedules were absolutely irrational. This idea seems very rational."

'Adapt or find another job'

Government offices have until the beginning of April to comply with the new work schedule. Workers must fulfil their eight-hour shifts between 7am and 6pm, with just one hour for lunch.

Officials have warned that those unwilling to adapt will be fired.

As Mexico has become increasingly industrialised the traditional siesta has not been as restful as it was in years gone by.