Commonwealth Bank's New Zealand subsidiary ASB has announced that customers with pre-approvals for high loan-to-valuation ratio mortgages must "use them or lose them" within 10 days, in its most drastic measure yet to slow lending to meet the Reserve Bank of New Zealand's new "speed limit".ASB apologised to customers for withdrawing pre-approvals not used by October 4 and asked them to revisit the bank to either increase their deposit or look for a cheaper house. The RBNZ's limit on high LVR mortgages kicks in from October 1, but banks have large numbers of pre-approved mortgages that have yet to be drawn down or expire within six months of issue.The RBNZ has given banks a six-month window from October 1 to reach the limit, which is that banks cannot lend more than 10 per cent of their new mortgage flow in the form of mortgages with LVRs of over 80 per cent.ASB was one of the most aggressive banks issuing high LVR loans from mid-2012 to early 2013 as it fought hard against an attack for market share by ANZ in its home market of Auckland. More than 70 per cent of ASB's net new mortgage lending was in the form of high LVR loans in some quarters during this period, although the net new lending measure isn't directly comparable with the new mortgage flow limit set by the RBNZ.ASB cited the RBNZ's speed limit in its announcement to brokers, saying the withdrawal of pre-approvals was being done "in order to comply with the lending restrictions being implemented by the RBNZ." It said it had to comply with the restrictions "like all New Zealand banks" and that it was a condition of its registration as a bank. "We appreciate that this will be disappointing for customers who are impacted and we apologise for any inconvenience caused," said ASB's general manager for products and strategy, Shaun Drylie.However, no other bank has yet to follow ASB's withdrawal of pre-approvals.Westpac said it was monitoring the situation. BNZ said it was honouring existing pre-approvals given its current flows and conversion rates. ANZ said it was honouring its pre-approvals and was still considering applications for new high LVR loans.ASB's move was a surprise. The bank's chief executive, Barbara Chapman, said last month the bank had "dialled back" the intensity of its high LVR lending since the RBNZ indicated in June it would limit their growth, but said ASB was unlikely to be affected more than other banks.