Margin pressure has dictated the pricing responses of the major banks to the Reserve Bank's latest 0.25 per cent official rate cut, with none of the market leaders delivering more than 15 basis points of rate relief to borrowers exposed to standard variable rate mortgages.Westpac and ANZ yesterday announced they would transmit cuts of only 15 and 14 basis points, respectively  - in defiance of urgent public calls from federal treasurer Josh Frydenberg for them to deliver the full benefit of the official move.  The public reaction has been particularly savage towards Westpac, which has passed on aggregate cuts of only 0.55 per cent  - the least of the major banks - since the RBA began reducing the cash rate in June.Westpac, arguably, is under the greatest margin pressure of the majors and chief executive Brian Hartzer has made a conscious decision to preserve the company's bottom line earnings over the next six months.The bank's net interest margin, excluding treasury activities, fell by 11 basis points in the March half.  Customer remediation costs were a key driver of the margin slide that underpinned a 24 per cent dive in net profit to A$3.17 billion.Despite withholding rate relief from borrowers, Westpac's anaemic loan growth suggests that shareholders are still facing the prospect of a cut to the final dividend when Hartzer unveils the full year profit early next month. Over the last 12 months each of the major banks has grown their aggregate lending books at less than the system growth rate, a trend that almost ensures their second half earnings  results before one-off items will be lower than the 2018 final half performances.According to GoldmanSachs analyst Andrew Lyons, CBA has outperformed its peers by managing to grow overall lending 0.8 times average system growth in the year to the end of August.ANZ was next best, having expanded total lending by 0.7 times the industry average, while growth at Westpac and NAB was barely apparent in nominal terms. Flagging volumes mean that aggressive margin management is one of the few remaining levers available to bank executives to preserve or retrieve interest revenue in the near term.Frydenberg yesterday postured that the major banks should follow the example set by small lenders such as Athena Home Loans that have promised to deliver the full benefit of the 0.25 per cent official cut to variable rate borrowers.In an interview with Channel Nine's Ross Greenwood after CBA and NAB revealed they would only pass on part of the RBA reduction, Frydenberg called on borrowers to protest the major banks' repricings."Well, the banks have a lot of explaining to do, Ross," Frydenberg said."Because this is very disappointing by the banks and customers should vote with their feet. Now, some of the smaller lenders have actually passed on this rate cut in full … "So, people should shop around, get the best deal, but also make their displeasure known to their banks." However, there's little doubt that the fault lines of margin pressure are now extending beyond