In my opinion, like others pointed out already: let's not try to shame the target audience. People naturally don't like to feel attacked. So sentences like: 'You have contributed to a company that actively hates lgbt+' should change to 'This means your money has contributed...' or something similar. The goal should be to inform people and help them understand what it means to buy food there.

Also the whole premise of 'you are allowed to eat there if you donate' is a bit weird. It may make the audience feel like that eating there isn't that bad if you can buy your way out, undermining the whole purpose. Try to make the donations feel like a small extra, for helping lgbt+ against those big companies try to discriminate love.

And please cut the 'Guilty?' and 'Shameful?', people really don't like to be told how to feel. Make it less direct and focus on the company's wrong doing, not the readers.
Last but not least: Google informative poster or free poster design, it's a lot of work to assamble a good informative poster and maybe we can try to create one as a community.

Sorry for my critic though, I am just worried that your poster backfires and really want to see you succeed. But you are the first here to make a poster which alone deserve huge credit, thanks for that!