The study, Life after death: six steps to improve support in bereavement, found a third of employees who were bereaved in the past five years, do not feel their employer treated them with enough compassion.
It also found more than half of employees said they would consider leaving their job if their employer did not provide adequate bereavement support.
Campaign group Change Bereavement Leave has been urging the Government to give employees the legal right to paid leave if they have suffered a family bereavement.
The founder of the group, Lucy Herd, began the campaign in 2010 after her 23-month son, Jack, drowned in their garden pond. Her partner at the time was only allowed to take three days off work by his employer – one of which was for the funeral.
A study conducted by Change Bereavement Leave found seven out of 10 UK employees would back a national guaranteed minimum of paid leave.
The NCPC study, which was done in partnership with Dying Matters Coalition and National Bereavement Alliance, found 87% agreed that all employers should have a compassionate employment policy, including paid leave, flexible working and other support.
NCPC chief executive Eve Richardson said the costs of bereavement are "too great to ignore" to individuals and society.
"Employers have an important role to play by being compassionate and having a bereavement policy in place," said Richardson. "They should also ensure they support their managers so that they're confident in having sensitive discussions about end of life issues with their staff."
Dawn Chaplin, National Bereavement co-founder, said: "Learning to live with the loss of someone close is one of the most painful experiences we can encounter, and society's response often makes it even harder.
"There's an urgent need to improve access to bereavement services and to ensure that people who have been bereaved are not ignored or left isolated."