DENVER, Colo. -

Xcel Energy is warning its customers of a scam they may affect Colorado residents.

The company says an illegal customer contact effort may target senior citizens in Colorado, particularly in the Denver Metro area.

As part of the scam, a phony customer service agent may contact an Xcel Energy customer to explain that his or her monthly electricity payment has been received but the check was not signed. Customers are then asked for a credit card number to pay the bill.

Investigators have not determined how many customers have been contacted by the bogus company but speculate that seniors may be a primary target because of their propensity to make payments by check.

Xcel Energy urges its customers to simply hang up if they are called under the false pretense of unsigned checks requiring credit card numbers.

If any customers have been victimized by this scam, they should contact their credit card company immediately as well as their local police department.

If customers have any questions or concerns regarding the company's bill payment policy, they can contact Xcel Energy at 1-800-895-4999.