The C.L.A.S.S.E. student federation voted against Charest's proposal to stretch the $1,625 tuition increase over seven years instead of five and boost the loans-and-bursaries program.
The decision was hardly a surprise coming from the hardline group, which has pushed for a continued freeze on tuition levels.
"Student associations haven't been on strike for 11 weeks to be left with a tuition increase," the group's spokesman, Gabriel Nadeau-Dubois, said Sunday.
Two other major student groups were still debating the offer, with one expected to make a decision on Monday and another later in the week. The leaders of both groups, however, have already indicated their members are likely to reject the deal.
Meanwhile, more demonstrations were held in Montreal and across the province Sunday.
For a sixth evening in a row, protesters marched through downtown Montreal. Like the night before, and in contrast to the vandalism and clashes with police seen in the middle of last week, there were no major incidents as several thousand people took to the streets.
The crowds have gotten progressively smaller, though, since the massive evening march on Friday after Charest made his offer public.
As the dispute enters week 12, about a third of Quebec students are still avoiding classes, but most have chosen to return to school.
Still, the Quebec Liberals don't appear to see an end in sight to the conflict.
They decided to move a party convention scheduled for next weekend from Montreal to quieter Victoriaville to try to avoid protesting students.
Earlier this month, protesters managed to get into a convention centre in Montreal, leading to a showdown with riot police and delaying a speech from Charest for about an hour.
It appears protesters will follow Charest on the two-hour trip northeast. A student group declared in a tweet Sunday they would shuttle students there by bus.