Alberta's first potential trades strike in a quarter century could impact the booming province's reputation for providing a reliable investment climate to energy companies, an economist said Wednesday.

"Oil and gas companies look at investments all around the world and they weigh the factors, such as labour costs," said Todd Hirsch, chief economist at ATB Financial.

"If Alberta is starting to be seen as place where there is a continual threat of strikes, that will weigh into their decision," he said. "They're not going to pull up stakes out of the province, but it will weigh into their decision on how attractive is the Alberta investment climate."

Some 25,000 skilled workers, including pipefitters and electricians, began casting ballots Wednesday in strike votes that could result in construction halting at unionized work sites in the oilsands and Alberta's two largest cities.

Results of the votes will be sealed until after the iron workers union holds its vote July 13.

The looming labour unrest among trades is the first in Alberta since 1982, when the government of Peter Lougheed created legislation grouping 10 building trades unions that negotiate with employer associations for contracts that apply across the province.

Under the province's labour law, none of the unions may take a strike vote unless 60 per cent of unions with unsettled contracts opt for a strike vote.