The majority of home care staff polled believe the service is not sufficient to meet the needs of those they care for, in terms of the time they can spend and the quality of care they can provide, Unison Scotland said.
The survey also reported high sickness levels, both physical and mental, among staff, amid declining pay and conditions and low morale.
The study, entitled Scotland: It's Time to Care, was based on responses from more than 300 home care workers across Scotland.
The survey found 44% of home carers were limited to specific times to spend with their clients.
To compensate, some workers stayed on in their own time or went late to the next person, while others told the survey they would cut back on the tasks they were able to carry out.
Half of workers said they are not reimbursed for travelling between client visits.
Scottish Labour's health spokesman Neil Findlay said: "It's utterly shocking that the people we rely on to care for our elderly and vulnerable are very clearly in a state of despair."
A spokesman for the Care Inspectorate said: "While our inspections show that the majority of care services perform well, we do not hesitate to take action where necessary and have powers to close failing services if they don't improve."
A Scottish Government spokeswoman said: "This Government is absolutely committed to ensuring that our older population get the support they need to stay in their own homes for as long as possible."