A strike at U.S. refineries by the United Steelworkers union isn't curbing operations at the affected plants, a monitoring group said.

Labor talks between USW and refineries, represented by Shell, broke down during the weekend, prompting the union to call for a work stoppage at seven U.S. refineries. Union officials said they had "no choice" but to call a strike, blaming the industry itself for the stalemate.

Genscape, which monitors refinery operations, said it's seen no major operational changes at refineries impacted by the strike.

"Barring any surprises, normal operations are expected to continue at the refineries where workers are striking," the group said in a Tuesday briefing on the industry impacts.

Genscape said strikes at refineries usually don't impact operations because refining companies have contingency plans in place to adjust to a work stoppage.

About 4,000 workers are on strike.

Tesoro Corp., which operates three refineries where workers are striking, said it's able to meet its contractual obligations despite the work stoppage.

"We intend to safely operate our refineries with fully qualified personnel and are confident in our ability to continue to responsibly produce transportation fuels to meet the needs of our customers," Tesoro Vice President Keith Casey said in a statement Monday.

There's been little word from USW or Shell on the status of the talks as the strike continues.