DENVER (AP) — Colorado regulators are warning real estate agents not to keep listings away from the market.

The Denver Post reports that Colorado’s hot real estate market is boosting the practice of brokers putting up signs saying listings are “coming soon.” The designation can help real estate agents find sellers before the listings go public.

The Colorado Real Estate Commission issued the warning because the practice can be bad for consumers. Because the full market can’t bid, sellers might not get as much as they could. Agents are able to take a commission from both the buyer and the seller.

Regulators say the practice has become widespread over the last six to eight months.

No agents have yet been punished for using such tactics, but they could face reprimands or fines.