Last month I looked at dispute resolution, one of two major employment changes that came into effect this month. Now I turn my attention to the other: the extension of the right to request flexible working to parents of children aged up to 16.

Its birth has not been easy. There was a 'will it, won't it' moment when Peter Mandelson announced a review of all regulation in light of both the recession and a concerted campaign by business groups to, if not bury it, at least postpone its introduction. But, unlike other family-friendly policies quietly swept under the carpet for the time being, this legislation is alive and kicking - and an extra 4.5 million employees are now eligible.

According to Sainsbury's HR director Imelda Walsh, who undertook the independent review into extending the right to request, allowing parents to ask for flexible working is the right approach. "Protection for business to say no is robust," she says. "Some jobs are time and location-dependent, such as till operators. But the Government wants as many people in work as possible and people want to work, have a family and a life."

Indeed, those who have been moaning the most - small and medium-sized businesses - often offer flexible working already, they just don't call it that. What they really don't like, however, is the compulsion to consider it.

Minister for employment relations Pat McFadden stresses it is a right to request, not have. "The reason we made it legislation is to give some sense of priority to requests. We've moved a long way from when the work pattern was one where the mother spent years staying home bringing up children."

So what does this change mean for you? If you want to refuse a request you need one of these grounds: burden of additional costs; detrimental effect on ability to meet customer demand; inability to reorganise work among existing staff; inability to recruit additional staff; detrimental impact on quality; insufficiency of work during the periods the employee proposes to work; detrimental impact on performance; and planned structural changes. Most employers should be able to justify refusal using one or more of these criteria.

However, as Matt Jenkin, head of the employment team at Morgan Cole, points out: "The bite for those who refuse a request is the potential for claims of sex discrimination and the exposure to significant awards of compensation that are not subject to any cap."

A policy requiring a job be performed on a full-time basis only may be seen as having a disproportionate impact on women, thereby amounting to indirect sex discrimination unless it could be objectively justified.

Siân Harrington is editor of Human Resources magazine.