As the West's population ages, so employers are going to have to take much more account of the needs of workers who also care for elderly friends or relatives.
According to research by academics at Britain's University of Sheffield, one in seven working women and one in 10 men currently provide unpaid care, and this number is set to increase.
The research was commissioned by the charity Carers UK as part of its Action for Carers and Employment campaign. It was funded by the European Social Fund.
The study estimated some nine million people will need to provide care for family and friends in the future, many of whom will be men at the peak of their working lives.
Millions of people will be struggling to combine unpaid caring responsibilities with paid employment, it added.
A recent survey by Carers Week also found that two thirds of carers believed that their careers had suffered because of their caring role.
It is also calling for reliable everyday services at home and in the community, dependable, planned respite support and emergency and crisis relief.
"If carers are to continue to carry the lion's share of care while remaining active in the labour market, it is critical that there are good services to support them," said Imelda Redmond, chief executive of Carers UK.
"Say, for example, the day centre transport for your disabled child is late, or the home care service for your frail, elderly mother is not reliable or sensitive, a carer does not have a choice Ė work will always come second to the person they care for," she added.
"In 20 years' time there will be almost seven million people aged 75 or older in the UK. Many will not be in good health. With figures showing that our economy will need to draw two million additional people into employment, this survey clearly indicates that we are facing an issue that could well become a crisis Ė and we need to tackle it now," she stressed.