From Sunday, under the European Working Time Directive, the number of hours junior doctors can work will be limited. BBC News Online examines the directive and what it means for doctors and other UK workers.
What is the working time directive?
The directive is a European Union initiative designed to protect workers from exploitation by employers.
It lays down regulations on matters such as how many breaks employees can take, and how much holiday they are entitled to.
The directive's headline regulation is aimed at limiting the average working time for employees in the European Union to 48 hours a week.
The regulations became law in the UK in October 1998 but some groups of workers, such those working in transport and junior doctors, were exempted from the directive.
However, as far as junior doctors goes this exemption starts to be eroded from Sunday.
So junior doctors will work fewer hours?
In theory, yes, their hours will have to fall to 48 per week by 2009, the government has said.
Doctors hours should fall to 48 per week by 2009
On Sunday, as a stepping stone towards the 48 hour target, NHS trusts are expected to ensure that no junior doctor work more than 58 hours.
The directive also sets new minimum rest requirements for doctors in training.
However, research by the NHS confederation indicated that as many as one in six NHS trusts did not expect to meet Sunday's deadline for all trainee doctors to be working 58-hour-week.
They have known about this for some time. Why are there problems?
The changes mean hospitals have had to review working arrangements. Currently doctors are supposed to work a 56 hour week.
Although this looks a more demanding target, it isn't because while it includes time such as that spent on the wards or operating, it does not include the time they spend asleep but on-call in the hospital so they are available if needed.
The EU regulations do, so trusts have had to replace on-call arrangements with a shift system, which in many cases requires more doctors.
This has proved problematic in some areas such as paediatrics and maternity where there is a shortage of medics.
What will happen if trusts do not comply with the directive?
They could be fined up to £5,000 by the Health and Safety Executive. However, the HSE is likely to be more lenient if it believes the trust is doing all it can to cut doctors' hours.
But the British Medical Association has said it will back doctors working over 58 hours who pursue legal action.
Are other kinds of doctors covered by the rules?
Senior hospital doctors are. But GPs will not be because they are self-employed.
My partner works more than 48 hours a week in an office job, is this illegal?
Probably not, as there is an opt-out clause in the directive.
The opt-out means that workers can put in more than an average working week of 48 hours if they have agreed to do so with employers.
However the "opt-out" is under attack.
Ms Diamantopoulou fears UK staff work too long
The TUC would like to see it go and Anna Diamantopoulou, the European employment commissioner, has said UK companies could be guilty of abusing the opt-out and forcing staff to work longer hours.
Unions say more than 3 million men in the UK work more than 49 hours a week, almost one in four of the male workforce.
The figure for women is far lower at about 5.5% of the workforce, partly due to higher numbers working part-time.
But the Confederation of British Industry (CBI) denies that abuse is taking place, and the conciliation service Acas has concluded that the directive is not a source of disharmony in UK industry.
Is the opt-out likely to come to an end?
The European Union has consulted on whether the opt-out should remain and is likely to announce a decision on its future in late September.
The EU has outlined four options for the future of the opt-out.
Phasing out of the opt-out
Alleged abuse by employers clamped down upon
Opt-out only allowed following an agreement between employers and unions or the workforce as a whole
Individual employees can continue to put in more than an average working week of 48 hours if they have agreed to do so with employers