DoorDash will require its drivers to verify their identity more often as part of a larger effort to crack down on unauthorized account sharing.

DoorDash has been under pressure to ensure its drivers are operating legally. Over the summer, it pledged to do a better job identifying and removing dangerous drivers after a flood of complaints of dangerous driving from cities. Officials in Boston, New York and other cities have said that in many cases, people with multiple traffic violations continue making deliveries using accounts registered to others.

The San Francisco delivery company said Thursday it has begun requiring some drivers to complete real-time identity checks immediately after they complete a delivery. Previously, drivers were occasionally asked to re-verify their identity before or after a shift. The new system has been introduced in Los Angeles, Denver, Seattle and other cities and will roll out more widely next year.

DoorDash said it has also developed an advanced machine learning system that can flag potential unauthorized account access, including login anomalies and suspicious activity. If the company detects a problem it will require the driver to re-verify their identity before they can make more deliveries.

Before U.S. drivers can make DoorDash deliveries, they must verify their identity with a driver's license or other government-issued identification and upload a selfie that matches their identification photo. They also must submit to a background check, which requires a Social Security number.

But the company has found that some drivers are getting around those requirements by sharing accounts with authorized users. In some cases, drivers who haven't been authorized to drive for DoorDash are paying authorized users for access to their accounts.

Some federal lawmakers have also demanded that DoorDash and other delivery apps do a better job of keeping illegal immigrants off their platforms. Republican U.S. Sens. Marsha Blackburn of Tennessee, Mike Braun of Indiana and Ted Budd of North Carolina sent letters to delivery companies in April asking them to crack down on account sharing.

"These illegal immigrants are delivering food directly to consumers' doors without ever having undergone a background check and often without even using their real names," the letter said. It added that working illegally can also be dangerous for migrants, creating the potential for exploitation and abuse.

DoorDash won't estimate how many drivers are using shared accounts, but said its safeguards are effective. Last year, it began asking drivers to re-verify their identities monthly by submitting a selfie. The company said it is now asking more than 150,000 drivers to complete selfie checks each week, and it's removing them from the platform if they don't comply.