Funeral workers in the UK who earn less than £15,000 a year are demanding a 25% pay increase.
The Co-op did not want to comment on negotiations
Representations on behalf of the Co-op funeral workers were due to be made by union chiefs on Wednesday.
The Transport and General Workers Union (T&G) said even if they get the increase, a worker for the Manchester-based company would still only get a basic salary of just over the £15,000.
They claim the 2,600 workers it employs are "grossly underpaid and undervalued".
The Co-operative Group's funeral service carries out more than 20% of all funerals in the UK.
The T&G's Ian Crawford said many people regarded funeral workers as the UK's fourth emergency service.
He added: "Our members have to deal with bereaved families as well as having to remove the deceased at any time of the day or night, 365 days of the year.
"They are paid less than £6 per hour for this sensitive work.
"The low pay levels have led to much frustration and we are prepared to campaign hard for a substantial pay increase."
A Co-op spokesman said the company did not want to pre-empt the pay discussions.