For years, one of the easiest way to earn large amounts of miles has been churning credit cards. Some issuers keep awarding signup bonuses no matter how many times you apply.

There are even reports of successfully obtaining new United Visa cards every 34 days or so — along with the 25,000 bonus miles for new cardholders (on both the personal and business cards, with fee waived the first year!) each time.

FirstUSA, which was acquired by BankOne, and is now Chase has been famous for allowing this on all of their co-branded cards — not just United, but also British Airways, Priority Club, Marriott, Southwest, etc.

Citibank’s American Airlines co-branded products have been easy to churn, and Bank of America cards like the USAirways Visa have as well.

There’s always a discussion of affect on your credit rating (increasing unused available credit increases your score, reducing average age of your accounts reduces your score, and often new requests for credit will lead to a temporary dip). But for those not in immediate need of a new mortgage this has been a very, very lucrative technique.

Now there are reports on Flyertalk that Chase may be wising up, at least with the United co-branded cards.

Details are still unclear — some have reported getting letters saying they won’t receive their signup miles because they’ve gotten the bonuses in the past, though there’s even a report of getting that letter but still getting the miles anyway.

Another report is Chase claiming they’ll remove the bonus miles from your account if you cancel the card, though that’s been a claim which has persisted without basis in fact for years — is it finally true?

Finally, I haven’t yet seen reports of this with other Chase co-branded products (or Citibank or Bank of America, for that matter). If the end of the game is in fact near for churning the United Visa, will the same be true for other credit card products as well?

A truly important new development, though facts at this stage remain unclear.