Starting Tuesday, Minnesota, the first state to require biodiesel be blended with diesel sold in the state, will require all diesel fuel in the state to contain 10% biodiesel. An exception will be made in the winter, when the requirement will be 5%.

The state trucking association criticized the move.

"We will be alone in the nation with a 10 percent mandate," John Hausladen, president of the Minnesota Trucking Association, told the Pioneeer Press. "We believe that the biodiesel industry is mature and can stand on its own. It does not need a mandate now, and it's time to phase out the mandate, not increase it."

Previously, the state required diesel fuel to contain at least 5% biodiesel -- 2% during the winter.

Biodiesel in this country is most often made from soybean oil, and Minnesota ranks third in soybean production in the nation.

When biodiesel made its debut in Minnesota nearly a decade ago, some poor-quality fuel led to clogged fuel filters, angry truckers, and emergency waivers of the new law. However, the biodiesel industry says the quality problem has long been solved.

The problems did result in delays for the higher blends. Originally, state lawmakers wanted all diesel fuel to contain 10% biodiesel by 2012 and 20% by 2015.

A B20 mandate is still on the books for 2018.

Hausladen noted that some industries are exempt from the mandate, including railroads, mining and logging.

Sixteen other states now have mandates or tax incentives to blend biodiesel with petroleum-based diesel, according to the National Biodiesel Board. Illinois offers a tax break to blend biodiesel at 10 percent or more, but only Minnesota mandates that high of a blend.

The move comes as nationally, biodiesel advocates are pushing the Obama Administration to continue growing biodiesel volumes under the Renewable Fuel Standard.

We asked engine makers whether the new mandate should be of any concern. Mack and Volvo said the use of biodiesel up to a maximum of 20% (B20) in and of itself, will not affect the manufacturer's mechanical warranty as to engine and emissions system related components, provided the biofuel used in the blend conforms to ASTM D6751, B1 to B5 blends conform to ASTM D975, and B6 to B20 blends conform to ASTM D7467.