Democratic U.S. Sen. Amy Klobuchar of Minnesota has joined with Republican colleague Sen. Charles Grassley of Iowa to push federal investigations of alleged restrictions on ethanol sales by the nation's major oil companies.

The senators cited a recent report by the Renewable Fuels Association, a trade group representing the ethanol industry, that claims name-brand oil companies unfairly limit ethanol sales at service stations selling their products.

Klobuchar and Grassley have written to Attorney General Eric Holder and Federal Trade Commission (FTC) Chairwoman Edith Ramirez, asking them to investigate a number of charges for possible legal and regulatory violations.

The senators are seeking "a substantive evaluation of your conclusions regarding possible anti-competitive behavior by certain oil companies and any proposed solutions or actions the DOJ [Department of Justice] and FTC will take ..."

Among the renewable fuels group's allegations:

• Brand-name service stations can sell only products provided by the oil company.

• Sales quotas of branded products discourage the sale of ethanol.

• Requirements to store multiple grades of branded gas eliminate the ability to store and sell ethanol.

• Oil company demands that ethanol pumps be labeled with "intimidating" warnings about how the fuel can hurt engines.

• Forcing dealers to isolate E85 pumps that deliver fuel that is 85 percent ethanol.

JIM SPENCER