FRESNO, Calif. (AP) — Regulators in California took a pivotal step on Monday toward becoming the first state to require the popular weed killer Roundup to come with a label warning that it's known to cause cancer.

Officials announced that starting July 7 the weed killer's main ingredient, glyphosate, will appear on a list California keeps of potentially cancerous chemicals. A year later, the listing could come with warning labels on the product, officials said.

However, it's not certain whether Roundup will ultimately get a warning label.

Monsanto, the chemical's maker, has filed an appeal aft...