Lawyers are warning employers that government plans to extend paternity leave could have a serious financial impact on their businesses.

The Work and Families Bill, which is expected to be published this week, will give a father six months unpaid leave if the mother forgoes the equivalent maternity leave. This would be an extension of fathers’ rights, as they are now entitled to two weeks of paid leave.

Edward Goodwyn, a lawyer at Pinsent Masons, said: “Firms would be at risk of losing key staff with specialist knowledge for long periods of time. If the leave falls in the middle of a complex project there could be huge disruption, both in terms of the costs of employing a temporary replacement and the administrative burden of bringing a replacement up to speed on the project.”

He said that administrative costs could also be incurred at the planning stage and that small firms might be hit especially hard, as they would less able to absorb losses.

However, a Construction Confederation spokesperson said that many in the industry were not worried by the proposal for unpaid leave. He said: ”In theory the industry would be ripe for it to have an impact, but in practice not many will take it up because of financial loss of earnings.”

Naomi Branston, a lawyer at Taylor Wessing, said the proposal would not be affordable for many families. She said: ”Frankly, given the already poor take-up of parental leave, which is also unpaid, it may be that employers are worrying too much.”

If it falls in a complex scheme there could be huge disruption

Lawyer Edward Goodwyn

However, she warned that the construction industry might find it harder to comply with the legislation than other sectors.

She said: “In this industry the proportion of women to men is still quite small so perhaps there is less experience in dealing with flexible working and taking time out for family.”

She said that the legislation was likely to protect fathers from any detrimental response from employers, such as unfair dismissal, if they take up paternity rights.