Amid growing worries about bird flu, the U.S. Department of Agriculture issued a federal order mandating the testing of the nation’s milk supply.

Regulators will now have to analyze samples from dairy farms or during the transportation or processing of milk thanks to the new government directive. Any instances must also be reported by private labs. California, Colorado, Michigan, Mississippi, Oregon, and Pennsylvania will be the first states to implement this testing program.

The virus is likely spreading through dairy farms. Infected milk can easily contaminate the milking area, and the virus can be carried by animals, humans, or even on equipment.

California health officials found possible bird flu in raw milk and cream from Raw Farm in Fresno. The farm is now quarantined, and some of its products are being recalled. While the risks are unclear, experts say drinking infected milk could lead to stomach infections. However, pasteurized milk is still safe, according to federal health officials. The federal government has also required testing of dairy cows before they’re shipped across state lines.

This order will complement one issued in April which required testing of lactating dairy cows before they were shipped across state lines.