NEW YORK (CNNMoney) -- After a couple years of buckling down and making on-time payments, consumers are starting to be a tad less responsible with their credit cards again.
Some of the country's major credit card issuers posted small increases in the number of credit card payments that were at least 30 days late in September, following a steady decline in delinquency rates since early 2009.
"Any time delinquencies go up I think it's a cause for concern, especially since we've seen a pretty good trend in declining delinquency rates," said Bill Hardekopf, CEO of credit card comparison site LowCards.com. "It looks like a signal that consumers are struggling."
Late payments among Capital One (COF, Fortune 500) customers have been rising slightly since June, when its delinquency rate rose to 3.33% -- from 3.32% in May. But last month, the delinquency rate jumped significantly -- to 3.65%, from 3.43% in August and 3.37% in July.
Increases at other issuers were smaller. American Express (AXP, Fortune 500), for example, saw its rate of late payments inch up to 1.5% in September from 1.4% in August. Discover (DFS, Fortune 500) posted a delinquency rate of 2.5%, up slightly from 2.49%, while Chase (JPM, Fortune 500) posted a rate of 2.53%, up from 2.48%. Bank of America (BAC, Fortune 500) saw its delinquency rate rise to 3.99%, from 3.96%.
While rising delinquency rates signal short-term trouble among consumers, things are still looking okay over the long term -- for now.
Credit card charge-offs, or defaults, occur when a payment is so late that a creditor deems it uncollectible -- usually after 180 days. Default rates among major issuers remain nearly half the level they were a year ago, and were still on the decline in September.
But if delinquencies keep rising, defaults are likely to increase as well, said Hardekopf.
What's more, new debit card fees could encourage people to rely more on credit cards, leading to more credit card delinquencies and charge-offs, he said.
Not all experts think September's higher delinquency rates are a sign of trouble, though. Odysseas Papadimitriou, CEO of CardHub.com, said that an average delinquency rate above the 4% mark is to be expected.
Right now, the rate of late payments remains well below historical levels. The 10-year average delinquency rate is about 4.6%; the 6.6% peak was hit in February 2009, said Papadimitriou.
"There's no question it's going to go back up to an average level," he said, adding that delinquencies have now been dropping for two and a half years.
After racking up debt in 2008, huge numbers of consumers ended up becoming delinquent or defaulting on loans in 2009. But once this debt was written off and these people were taken out of the picture, the delinquency rate began declining and hit a bottom this summer. And now it's on it's way back up, Papadimitriou said.
"It's when we start crossing that 4.5% threshold that there's cause for alarm," he said. 
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