PepsiCo has paid strong dividends for decades, but will its growth slow? Image source: PepsiCo.

Dividend investors love it when the stocks they own increase their quarterly payouts. In fact, many of the favorite stocks that dividend investors gravitate toward consistently raise their dividends each and every year. Yet even though any dividend increase is a good thing, companies that decide to slow the rate at which their dividends grow over time could be sending a message of tougher times ahead. With that in mind, let's look at three stocks that have considerably slowed their dividend growth in 2015 compared to past years to see if investors should worry.

Philip Morris International holds its breath
The tobacco industry has been a strong source of dividend growth for decades, as cigarette makers have repeatedly defied calls that their business would inevitably succumb to declining sales volume as more smokers decide to quit. Since going public in 2008, Philip Morris International (PM 2.82%) has more than doubled its quarterly dividend and still has an impressive 5% yield.

Source: Philip Morris.

Yet what has hit Philip Morris International (PM 2.82%) hard lately has been the strength in the U.S. dollar, which has exacerbated the impact of shipment-volume declines. During the first half of 2015, adjusted earnings per share have fallen about 9%. Perhaps in response, Philip Morris recently decided to raise its quarterly dividend by only 2% to $1.02 per share, marking a considerable slowdown from the 6% boost in 2014 and a 10% rise in 2013.

If the dollar rebounds, it should give Philip Morris the ability to accelerate future dividend increases. For now, though, the dollar's strength could keep hurting dividend investors who hold the tobacco giant's shares.

PepsiCo loses a little of its fizz
(PEP 1.08%) has been a dividend star for decades, with a consistent track record of raising its payouts over time. The company kept up that streak with a 7% increase in its dividend, and the drink and snack giant now pays $0.7025 per share, amounting to about a 3% yield. Yet some were disappointed that PepsiCo didn't make a more aggressive increase in light of its decision in 2014 to pay out 15% more than in 2013.

In many ways, though, it was 2014 that was the outlier for PepsiCo in terms of dividends. At the time, activist investor Nelson Peltz had tried to get PepsiCo to spin off its soft-drink division, figuring that the snack business would fare better if it were separated from the controversies over the health effects of carbonated beverages. With PepsiCo returning billions to investors through stock buybacks in addition to maintaining a solid dividend yield, it's hard to fault PepsiCo for choosing not to sustain double-digit percentage dividend increases as well.

Wells Fargo faces a steeper slope
Banks saw big hits to dividends during the financial crisis, and even Wells Fargo (WFC 2.74%) proved to be no exception. Yet since then, the company has boosted its dividend on five separate occasions and now pays more than seven times as much as it did during the bust years of 2009 and 2010. However, Wells Fargo's dividend growth has slowed over time, and 2015's quarterly increase of $0.025 per share to $0.375 is the stingiest increase in a long time, with the 7% raise representing a big deceleration from 2014's 17% boost.

Wells Fargo has had to deal with several challenges, however. First of all, the Federal Reserve's stress-test regime has put considerable restrictions on banks seeking to return more capital to investors, and it's been easier for Wells Fargo to use stock buybacks as a method for putting profits to work rather than permanent dividend increases. In addition, the bottoming of interest rates has led to a considerable drop in refinancing activity, which in turn has slowed Wells Fargo's mortgage origination business. None of these factors has killed off the bank's growth entirely. Yet with the stock now paying more in dividends than it did prior to the financial crisis, it's not unreasonable for Wells Fargo to slow down its growth rate in its payout.

Dividend growth is always good to see, but when growth slows, a stock deserves a second look. Slowing dividend increases don't necessarily signal an imminent decline, but it's helpful to take the opportunity to make sure you understand what's supporting the dividend going forward.