I was required to sign a photo release to stay employed at the company I work for. Is this legal?

I work for a non profit company that now requires employees sign a photo release to stay employed with the company. I asked why we couldn't opt out of having our pictures released and the reason given was " we had too many pictures that were unusable because of those who have opted out" This is a great company that does great things for the community but I don't want my photo used for advertising and this seems to be why they want to use employee photos. I think it is wrong to require this of us as employees.