This resembles symptoms of Septoria Leaf Spot, but that is not a disease we tend to see manifesting symptoms or causing damage this early in the season. Fusarium Wilt manifests differently than this. Are the tomato plants in the ground now, in a home greenhouse, or still indoors? Were they purchased recently from a garden center as transplants or older plants, or started from seed indoors earlier in the year?

If this is Septoria, remove the worst-affected leaves (especially lower leaves) and consider treating the plants with a copper-based fungicide, as noted in the linked page above. It won't be able to cure existing disease, but may help to prevent infection on still-healthy younger growth. Follow label directions for use, since several re-applications will likely be needed.

There is a chance this is not fungal at all but rather environmental stress damage, like from cold nights. If so, the plant will outgrow the damage without any need for intervention.

Miri

Okay, then given the source, it might actually be Septoria, so hopefully the fungicide will suppress infection spread.

Miri