The coalition Government has been urged to support the repeal of the Working Time Directive, which aims to limit workers' hours, because of its "negligible" value in tackling unhealthy workplace behaviour.
The Chartered Institute of Personnel and Development said employers were not convinced about the merits of the directive, which was intended to limit working hours to 48 a week.
Many workers opted out of the directive, while surveys consistently show that the UK continues to have a long hours working culture. The CIPD said the directive should be repealed under a review currently being undertaken by the European Commission.
A survey of 800 employers by the CIPD found that one in four gave no paid paternity leave above the statutory minimum, with only two out of five offering two weeks pay.
Mike Emmott, employee relations adviser at the CIPD, said: "While employers are supportive of the national minimum wage and a plethora of equality rights, they are yet to be convinced about the merits of the Agency Workers Directive and the Working Time Directive.
"The CIPD believes that the Working Time Regulations in particular have negligible value in limiting unhealthy workplace behaviour. We are, therefore, calling for its repeal in the context of the review currently being undertaken by the European Commission.
"The more intractable challenge to both the Government and employers lies in encouraging more working fathers to take up their entitlements to paid paternity leave. If flexible parental leave is going to become a reality, we need a step-change in the reward policies of UK organisations that encourages more fathers to take their statutory rights.
"This is something that will only be achieved through cultural change - and legislation is emphatically not the answer. The new Government will have to think imaginatively if it is to nudge and lead this change."
TUC general secretary Brendan Barber said: "Good employers that treat agency workers fairly have nothing to fear from the legislation coming in this autumn. But sadly there are too many employers who behave less well when it comes to temps, which is why unions campaigned long and hard for extra protection for agency workers. Similarly too many employees are still being put under pressure to work long hours by their employers, and excessive working time makes for unhealthy employees.
"Recent research has shown that over-long hours increase the risk of contracting heart disease, whilst the CIPD's own research indicates that a quarter of employees who worked long hours became ill. We shouldn't be allowing the UK's long hours culture to put the safety, health and well-being of workers at risk, and that must mean strengthening the working time rules not relaxing them."