The Detroit Hamtramck facility, where the 2013 Chevrolet Volt is made, is to pause production for four weeks, the second time GM has temporarily halted production.

The official Volt-haters society is surely throwing a huge party this week (if such people ever throw parties), but over here on the pro-EV end of the dial, the reasons for the holiday are less clear. A source at GM told InsideEVs that the closing is “to make room in the plant for the upcoming Impala, and it has nothing to do with the Volt really.”

InsideEVs offered some more juicy details. Apparently the Canadian Auto Workers Union (CAW) doesn’t share GM’s enthusiasm for building Impalas at D-Ham. A CAW spokesman told theGlobe and Mail that “the Impala is a Canadian-made vehicle; we own the rights to produce it in Canada and we’re going to continue to produce it in Canada.” The current CAW contract just happens to expire on the same day the Hamtramck plant is scheduled to be idled, which leads our colleagues to speculate that the move may be part of the sprouting rhubarb between GM and CAW.

Whatever the reasons for the production pause may be – caution, retooling or union intrigue – we’re not getting nervous just yet. GM says the plant continues to hire new workers, and plans to add a second shift early in 2013, to work on the Volt, Impala, and Malibu. And, as we reported at the end of July, the Volt is by far the best-selling plug-in – GM has sold 10,666 in the US year-to-date, and the Volt’s European cousin, the Ampera, is also a leader in its markets.

Image: GM