Nonprofit advocacy is legal! Nonprofits engaging in partisan politics (endorsing candidates) is not legal!
NOW is the time for all nonprofits to come to the aid of their citizens (yes, paraphrased)! It is a nonprofit's (BOARD) right and responsibility (see the 1st Constitution) to speak out to ensure that what a nonprofit believes in is preserved - that its constituents are not harmed. Your voice matters.
To learn more about the hows and wherefores of nonprofit engagement in advocacy check-out the National Council of Nonprofits as well as your own state nonprofit association of nonprofits. And don't wait. The time for protecting all that is important to your nonprofit is NOW. And Board members - this means YOU!