The New Rules of Call Blocking

For years, carriers have been expected to block illegal robocalls. But “expected” is not the same as “required.” The FCC has now closed that gap.

In March 2025, the FCC adopted new rules requiring all domestic voice service providers to block calls based on a reasonable do-not-originate (DNO) list. The effective date for this requirement was December 15, 2025.

This is a significant expansion of carriers‘ call blocking obligations—and it comes with real consequences for non-compliance.

What Is a Do-Not-Originate (DNO) List?

A DNO list is a database of phone numbers that should never originate calls. If a call appears to come from a number on the DNO list, it is almost certainly spoofed and should be blocked.

Examples of numbers on a DNO list:

– Numbers that belong to government agencies

– Numbers that belong to law enforcement

– Numbers that belong to other carriers

– Numbers that have been identified as frequently spoofed

The FCC‘s requirement: Carriers must use a “reasonable” DNO list to block calls. The FCC does not mandate a specific list—carriers can choose their own—but the list must be reasonable and effectively implemented.

Additional Call Blocking Requirements

The FCC‘s new rules go beyond DNO lists:

SIP Return Codes: Carriers must return Session Initiation Protocol (SIP) error codes when blocking calls, so that originating carriers know their calls are being blocked.

Exclusive Blocking Notification Code: The FCC has designated an exclusive code to notify callers when their calls are blocked, empowering them to address erroneous blocking.

All Providers in the Call Path: The FCC‘s rules apply to all providers in the call path, not just terminating carriers. This means intermediate providers and gateway providers also have blocking obligations.

The Enforcement Reality

The FCC is serious about call blocking enforcement. The Commission’s ever-increasing requirements build on a January 2025 Report and Order that imposed new requirements and fees for RMD filers.

What happens if you don’t block?

– Per-Call Penalties: The FCC has established per-call penalty standards for call blocking violations. Each failure to block can result in significant fines.

– Operational Disruption: If you are not blocking illegal traffic, the FCC may require other carriers to block all of your traffic.

– RMD Removal: Severe call blocking failures could lead to removal from the RMD.

The Gateway Provider Obligations

Gateway providers—carriers that accept traffic from foreign originating providers—have additional obligations:

Gateway providers must take “reasonable and effective steps to ensure that any foreign originating provider or foreign intermediate provider from which it directly receives traffic is not using the gateway provider to carry or process a high volume of illegal traffic onto the U.S.”

This means gateway providers must actively vet their foreign partners and block traffic from partners that generate illegal calls.

How to Implement Effective Call Blocking

Implementing compliant call blocking requires a systematic approach:

Choose a Reasonable DNO List: Select a DNO list that is comprehensive and regularly updated.

Implement Blocking Technology: Use technology to automatically block calls from DNO numbers.

Monitor Blocking Effectiveness: Regularly review your blocking to ensure you are catching illegal traffic without blocking legitimate calls.

Respond to FCC Inquiries: If the FCC contacts you about blocking, respond promptly and demonstrate your compliance.

Document Everything: Keep records of your DNO list, blocking decisions, and any challenges to blocking.

The Bottom Line

Call blocking is no longer optional for U.S. carriers. The FCC has mandated it, and enforcement is coming.

The December 15, 2025 deadline has gone past. Carriers that failed to implement reasonable DNO-based blocking face per-call penalties, operational disruption, and potential RMD removal.

At Microtalk, we help carriers implement compliant call blocking solutions that meet FCC requirements and protect your business from enforcement actions.

Does your carrier business abide the December 2025 call blocking deadline?