That's a total of 16 out of 19 candidates who are rejecting the talks.
On Thursday, Mr Sall promised to stand down at the end of his term on the 2 April - but failed to set a date for the election of his successor.
The group demanded that the poll be held before that date.
"We are calling for mobilisation," presidential candidate Aliou Mamadou Dia is quoted as saying by AFP news agency, adding that the group was working on an action plan to take place on Monday and Tuesday.
Earlier this month the president triggered a constitutional crisis when he postponed the election that had been due to take place on Sunday