Must grocery store employees ask customers to make donations?

My mom works for Vons and she is very disturbed by their newest fundraising campaing. She hates when people solicit her for donations at home, work or by phone. Now she is being told that she must ask every customer to make a donation to prostate cancer research. She has voiced her objections to her boss and he has told her that if she doesn't ask she will be suspended without pay. Now she feels threatened. When she called her Union representative about filing a grievence, they stated they would not support it. What can she do? Her contract does not state that she much raise funds for charities as part of her job description. Any advice?