I was in a similar situation, but it was for an org I volunteered with. They asked for help to prepare a meal for a large community meeting. They knew I was vegan, as were several other prominent members of the community.

When I showed up in the kitchen, they had a lot of veggies, pasta, potatoes, beans, lentils etc. I did a lot of chopping and prepping. Then, after the food was prepared they tossed bacon or cheese into just about everyting. Almost as if out of spite.

I stopped volunteering there and explicitly told them why. I was preparing food for a meeting that I would be attending and they went out of their way to make sure I could not eat it.

Worse yet, this org claims it is environmentally conscious and the rest of it, yet has a chicken coop right next to its greenhouse. The hypocrisy and stupidity was too much.

That said, it is a different matter if it is your job. I would not hold it against you if you went along until such time as you were able to find another job.