Failure to pass the bill could mean skyrocketing premiums that could drop home values, NAFCU's Brad Thaler says.
Measures would delay increases by perhaps four years if they gain passage.
Senate bill would delay NFIP-mandated increases except for second homes and businesses.
Letter says insurance firms must charge for true costs.
Hearing Wednesday focuses on affordability issues in National Flood Insurance Program rate hikes coming in October.
Amendment passed Tuesday would bar the rate increases by preventing FEMA from using federal funds to implement Sec. 207.
The amendment passed 281-146, and the appropriations bill was later approved by the full House and sent to the Senate.
GOP Rep. Randy Neugebauer asks for speedy approval from banking industry regulators, sparking calls for caution from some insurers.
Obama signed expansion into law over the weekend; Sandy claims cited as cause for concern.