It wasn't a good day for Weatherford International (NYSE:WFT). On Monday, the company reported a drop in its quarterly income and also that it's being probed by the Department of Justice relative to the possibility of improper sales of products and services.

For the quarter, Weatherford saw its income from continuing operations slide 6.4% to $176.5 million, or $0.51 a share, compared to $188.5 million, or $0.53 per share, a year ago. Net revenues for the quarter were up 18% year over year to $1.82 billion.

Weatherford, which provides a variety of drilling, completion, and production assistance to oil and gas operators, was hurt in the quarter by a substantial decline in drilling activity in Canada. The company thereby joins a league with other oilfield services companies, including Baker Hughes (NYSE:BHI), Halliburton (NYSE:HAL), and Schlumberger (NYSE:SLB), that have experienced a falloff in Canada.

In fact, while Weatherford's revenues in North America were up 5% during the quarter, the company said that growth in the U.S. rig count was more than offset by a 51% decline in the Canadian count. As a result, its North American operating income fell 13.5% from the year-ago period.

The Justice Department investigation apparently involves possible sales of products and services in sanctioned countries. Weatherford said that it's cooperating fully with the probe and that it cannot predict a likely outcome or the potential financial impact that might result from it.

I believe strongly that the world of oil and gas exploration and production will become infinitely more challenging in the years ahead. For that reason, I believe that at least proportional weighting in energy sector investments is a good idea for my Foolish friends. But while Weatherford long has been a member in good standing of the Houston-based oilfield services contingent, it still derives nearly half of its revenues (48.6% in the most recent quarter) from North America.

That concentration, coupled with the nascent Justice Department look-see, would lead me to shy away from the stock for the time being, despite the market treating Weatherford shares rather gently following the company's earnings release.

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Fool contributor David Lee Smith does own shares of Halliburton and Baker Hughes, but has no position in the other companies mentioned. He welcomes your questions or comments. The Motley Fool has a disclosure policy.