HOUSTON – Credit unions which use the PULSE EFT network, will see an average 20% increase in their PULSE interchange starting June 1, 2005 as the debit network adopts a tiered interchange structure similar to that used by MasterCard and Visa. Previously the network, which had been owned by financial institutions until it merged with Discover in January 2005, had charged merchants a flat fee of 18 cents per transaction along with a switch fee that Pulse kept as a revenue stream. Now the debit network has adopted a tiered structure which will have separate categories for grocery and general retailers and a number of tiers within each category, according to Cindy Ballard, a vice president for the network. The small switching fee PULSE charges will also increase, Ballard said. She declined to say how many tiers the network would use