Mortgage funders will have to confirm their access to warehouse lines through which they can continue to originate new home loans in order to sell any mortgage-backed securities to the Australian government.The Australian Office of Financial Management late yesterday published a request for tender for the planned investment. The deadline for the RFT is Friday week.Only banks and investment banks already registered with the AOFM may submit bids, and then only those that have led the sale of mortgage-backed securities in the past. They must also "intend to remain active in funding new mortgages through securitisation".As previously foreshadowed, the AOFM aims to invest in newly-issued RMBS as a co-investor, so proponents will have to find additional investors in the AAA-rated senior tranches as well as investors in the subordinated and equity tranches in the loan pools.The RFT spells out the parameters for the investment as maximum loan size of $750,000, maximum terms to maturity of 30 years, maximum loan to valuation ratio of 95 per cent and a weighted average LVR of 70 per cent. Low doc loans must comprise no more than 10 per cent of the pool.The AOFM will invest a maximum of only $500 million in any one issue.The AOFM expects to allocate one or two mandates quickly and expects to make the investment by the end of this year.The government at the weekend doubled the planned investment to $8 billion and reserved half for investment in mortgage bonds originated by non-bank funders.