NEW YORK (Reuters) - The attorney general for Washington D.C. has filed a lawsuit against an AT&T Inc T.N unit, seeking to recover consumers' unused balances on prepaid calling cards.

The suit claims that AT&T should turn over unused balances on the calling cards of consumers whose last known address was in Washington, D.C. and have not used the calling card for three years.

“AT&T’s prepaid calling cards must be treated as unclaimed property under district law,” the attorney general’s office said in a statement.

According to the attorney general’s office, that sum, known in the industry as “breakage,” represents some 5 to 20 percent of the total balances purchased by consumers who use the calling cards.

States and municipalities have often similarly used unclaimed property laws, known as escheat laws, to claim ownership of unused retail gift card balances.

A spokesman for AT&T declined to comment on the lawsuit.

The case is: District of Columbia vs. AT&T Corp, Superior Court of the District of Columbia.