I am generally in favor of payroll deduction programs that allow employees to contribute directly from their paychecks to charitable organizations.  The Combined Campaigns for governmental employees and United Way campaigns for both government and private employees are traditional programs throughout the country.  They can be effective and efficient ways to raise funds for important causes.

But you point out how a purely voluntary program can be abused, how employers can effectively mace employees into giving to causes they have no desire (or financial ability) to support. Even though it might not be illegal, your boss obviously has a conflict of interest and ought not to be using his or her position to compel conduct unrelated to your job.

If you are a member of a union, perhaps the union will lodge an objection.  If you have some sort of civil service protection, you may be able to weather the backlash individually.  If you are an at-will employee, you may want to see whether the district has a whistleblower protection policy that would protect you if you reported your concern to the district CEO or a member of the school board.  If other employees share your concern, a group of you might be willing to raise the issue directly with the boss, recognizing that you might have to take your chances on the reaction.  Unfortunately your situation is not unique and, if you want to keep your job, you will have to figure out how to deal with the situation with the least potential damage.