Grandparents in the UK should be given the right to request unpaid leave so they can combine looking after their grandchildren with their jobs, according to the Trades Union Congress.
Although many working grandparents play a key role in the care of their grandchildren, they are currently only entitled to take short periods of unpaid leave in an emergency, explained the TUC.
The TUC, which commissioned a YouGov poll, argued that new right to unpaid leave enjoys considerable support from both grandparents (42%) and parents (50%).
The trade union said the government has an opportunity to introduce unpaid leave for grandparents as the Children and Families Bill reaches its report stage in the House of Lords.
"The informal childcare that millions of grandparents regularly provide is one of the most important and unheralded forms of care in Britain today," said Frances O'Grady, the general secretary of the TUC.
She added: "The childcare provided by grandparents allows mums and dads to work, saves them money on nursery and childminder fees, and creates a special bond across different generations in a family."
In addition, the research revealed nearly three in five (58%) grandparents provide regular childcare without the child's parent or parents present, equivalent to nearly seven million grandparents across Britain.
The most popular reason grandparents gave for looking after their grandchildren, cited by 50%, was to allow the child's parents to work.
The TUC said this was the reason also given by 45% of mums and dads with children under 16 who are looked after by their grandparents.
The polling also showed that working grandparents are more likely (63%) to look after their grandchildren than retired grandparents (55%).
The report argued while grandparents have always played an important role in looking after their grandchildren, the record number of people now working into their late 60s means that many are taking on childcare responsibilities for a second time while they are still working.
With the average weekly wage higher for people in their 30s (£468) than for those their 50s (£427.80) and 60s (£320.90), some families may feel it makes financial sense for a grandparent to reduce their hours and provide informal care, rather than or in addition to a parent in order to ease the pressure on childcare bills, according to the TUC.
"Family life is changing and it's time that government and employers caught up," said Sam Smethers, chief executive of campaign group Grandparents Plus.
He added: "Grandparents are picking up the strain that families are under and providing an increasing amount of childcare. But they are under pressure themselves, working longer and struggling to combine paid work with caring.
"We risk a childcare gap emerging – with parents paying the price – if grandparents cannot afford to reduce their hours or can't get the flexibility they need. The solution is a period of grandparental leave and an investment in formal childcare."