Brokers fear DTIs could lead to confusion for lenders and borrowers, making the home lending process even more burdensome.
David Windler of the Mortgage Supply Company said his "greatest fear" was a rigid implementation of DTIs across the banks, not allowing lenders to take their varying lending capacity and risk appetite into account.
He also questioned how rental income would be classed as income, and to what extent consumer debt would be tallied up.
David Green of adviceHQ agreed.
"The interpretation and application of a DTI test is the key," he said. "What are they going to class as debt? And what are they going to class as income? What are the calculations and how do they change over time?"
Green added: "We have seen how simple policy statements can become complex in application with the latest changes to bright-line, aka capital gains, tax, and interest deductibility with the 143-page consultation paper.
"On a macro level, DTIs is further government intervention in a heavily regulated environment which detracts from the key issue: the lack of supply of land, builders, materials," Green said.
The Reserve Bank will consult lenders before adding DTIs to its regulatory toolkit.
The central bank has hinted that DTIs might not be needed if reimposed LVR restrictions and the Government's housing reforms take the heat out of the market.
Nonetheless, advisers are concerned about the direction of travel as regulation on investors mounts.
Kris Pedersen of Kris Pedersen Mortgages said the rules would hit large portfolios as well as mum and dad investors. Richer investors on higher incomes may be less affected than those groups, he said.
Pedersen said Finance Minister Grant Robertson was on "a crusade to beat up property investors".