Tax bills proposed in both the House and Senate would give hedge-fund managers a generous new tax deduction for charitable donations as a way to promote philanthropy.

Under the proposed tax-extender bills, hedge-fund managers would be allowed to receive a full tax write off for every dollar they donate to charity — up to 100 percent of their deferred compensation.

Other taxpayers are allowed to deduct donations up to 50 percent of their annual income.

Sen. Charles Grassley, the Iowa Republican who is the ranking minority member of the Senate Finance Committee, calls the proposed deduction for hedge-fund managers unfair.

“Everyone is obviously in favor of charity, but treating wealthy hedge-fund managers better than your average American makes no sense from a tax-policy perspective,” Mr. Grassley said in a written statement.