Whenever the Congress of the United States shall enact laws providing for the payment of supplemental or extended unemployment compensation benefits, the secretary with the approval of the Governor, is hereby authorized and empowered to enter into such agreements with the United States Department of Labor or such Federal agency as may be charged with the administration of such laws as may be necessary to obtain for the citizens of this Commonwealth the benefits of such laws. No such agreements may be executed if, as a result thereof, employers in this Commonwealth would be subjected to a tax burden under any Federal law imposing a tax on payrolls not applied uniformly to all employers subject to such law.