Mary Jane Rogers, a spokeswoman for Chase, says that issuing 1099-MISC forms isn’t new. The forms reflect payments for items like referral bonuses, which are given to customers who refer a friend to Chase, or a bonus for customers who sign up for paperless bank statements.

In Chase’s case, she said, the forms are likely getting attention from customers because the bank made errors in calculating the amounts on a “few thousand” forms and had to reissue them.

Some Chase forms sent this year showed much higher dollar amounts than expected, according to the credit card website Doctor of Credit. In some cases, the bank reported a bonus of 500 points as $500, which assigns a value of $1 per point — much higher than is typical.

Assigning a cash value to rewards points or frequent flier miles is a bit of a gray area since the value of points can vary depending on how the cardholder redeems them. But a value of 1 cent per point is common, said Brian Riley, director of the credit advisory service at Mercator Advisory Group. At a penny a point, 500 points would equal $5.

At Discover, card holders who earned $600 or more on “nontransactional” rewards are sent 1099-MISC tax forms, said a spokesman, Derek Cuculich. Those include rewards for referring a friend, a one-time cash back “match” bonus given to new cardholders and the “good grades” program, which offers statement credits of $20 a year to holders of its student card if they maintain a grade-point average of 3.0 or higher.

There haven’t been any recent public edicts from the I.R.S. on the topic, Mr. Zidik said. But banks may be influenced by a 2014 ruling by the United States Tax Court, which held that the value of an airline ticket bought with frequent flier miles that were received as a premium, in exchange for opening a bank account, must be included as income.

“The tax court case could likely be driving the banks to issue the 1099s,” Mr. Zidik said. The banks could also face penalties, he said, for not issuing the forms when required.