The Guernsey Voluntary Service says it won't be able to get people to its day centres, unless more volunteers come forward.
GVS manager Mandy Le Bachelet says older people who come to their social clubs at the Russells and the Jubilee Day Centre will miss out if they can't find more drivers:
"Everyday over the next month we are short of drivers to bring in our clients. This means they're isolated at home and we provide a three course lunch and they're missing out on that."
The Guernsey Voluntary Service uses 12 and 9 seater minibuses.
In Guernsey, a 9-seater can be driven by anyone who has held a category B car licence for at least two years, as long as they're not being paid to do it.
But for a 12-seater, a driver in Guernsey would need to hold a Category D1 licence, which involves a medical check up and a signed declaration from a doctor before the licence can be upgraded, at a cost.
The rules are similar to the UK, but the difference is that anyone in Britain who passed their test before 1997 can drive a minibus with up to 16 seats without applying for a licence upgrade.
Mandy Le Bachelet says applying the UK rules in Guernsey would make it easier to find drivers:
"You are able to drive a 16-seater minibus if it is not for profit or not for hire, which means that charities and sports and social clubs can actually rely on more drivers."
She says they have adapted one of their minibuses to avoid the need for D1 licence:
"Because of the difficulty in finding drivers with a D1 category licence, many organisations have either had to remove 3 seats from their minibuses to make them a 9-seater, as we have done, or going forward purchasing 9-seater minibuses, which is very similar in price to a 12 -seater. This is not very practical, especially for those who, like us, need a 12-seater minibus for our clients,"
The Guernsey Voluntary Service has placed online adverts to try to find suitably qualified volunteers for the coming weeks.
"I fear I cannot just sit back and hope the situation will improve in time, as our time is running out."