Pennsylvania's 12 casinos are protesting a proposed 33 percent hike in the assessment on their gambling revenues that pays that state's cost for regulating the industry.

The casinos estimated in a letter Thursday to Pennsylvania Secretary of Revenue Eileen McNulty that the increase would cause their regulatory costs to jump to $75 million from $56 million.

McNulty explained in a March 31 letter to casino operators that "the increase is necessary due to cost increases such as benefit, pension, and contractual salary increases."

The increase, to 2 percent from 1.5 percent of casinos' gross slot revenue and gross table revenue, is to go into effect July 1.

The casinos' letter referred to a 2014 analysis that found Pennsylvania's regulatory costs for casinos to be among the highest in the United States. The state's casino taxes are also among the highest.

The letter called the "surprise, unilateral determination to increase regulatory costs and expenses by 33 percent is a regettable departure" from a history of partnership between the state and the industry to raise money for property-tax relief.

The Pennsylvania Department of Revenue said it received the letter and was reviewing the concerns.