There are a number of ways in which an employer may support the charitable giving of its employees.
Some employers organize workplace giving campaigns. In most cases, these campaigns are set up to allow you to make automatic donations to non-profits through your employer's payroll system. Sometimes those campaigns are done independently, and sometimes they are done through a United Way or as part of the Combined Federal Campaign.
Some employers offer a matching gift program. There is a great amount of variety in how these are run, but in many cases the employer offers a dollar-for-dollar match if you fill out the appropriate paperwork. If your employer does not offer a matching gift program, consider asking them to start one.