The owners of Parx Casino, known for huge charitable donations, are fighting for a lower property-tax bill in Bensalem Township and have paid their property taxes under protest for the last three years.

The Bensalem Township School District said last month in a bond-offering document that Parx, including the race track, was by far the largest taxpayer in the township, accounting for 8.4 percent of school district assessments.

The total assessment for Parx, which is owned by Greenwood Gaming & Entertainment Inc., is $54.1 million. That translates into a market value of $426.8 million and an annual property tax bill of $10.1 million, according to the tax rate for 2013 published on Bensalem Township's web site.

The dispute centers on a 411-acre parcel that Greenwood bought for $56.9 million in 1990, according to a court document.

After Greenwood built Parx Casino, the Bucks County Board of Assessment Appeals increased the assessment of the property to $42.7 million from $11.8 million, a court filing says. After an initial appeal, the board of assessment dropped the assessment slightly, to $40.5 million in 2011.

That's when Greenwood subsidiaries Keystone Turf Club Inc. and Bensalem Racing Association Inc. appealed to the Court of Common Pleas. The companies argued in their 2011 lawsuit that the contested property's assessment should be $30.3 million. That would cut the company's annual real-estate tax by about $1.9 million, or about 19 percent, a year.

The Bensalem Township School District said in its bond prospectus that it expected the Parx tax appeal to be resolved in the next 18 months.

Carrie Nork Minelli, spokeswoman for Parx, said the company does not comment on matters in litigation.