The family of Glen Turner, the environment compliance officer murdered in 2014, says new native vegetation codes will diminish "the value of his life", and have appealed to the government to delay their introduction.

In a letter sent to NSW Premier Gladys Berejiklian and NSW Environment Minister Gabrielle Upton obtained by Fairfax Media, Mr Turner's widow Alison McKenzie and his sister Fran Pearce said the codes would give farmers "the opportunity of a lifetime ... to clear what they like and get away with it".

The pair were part of a briefing by Local Land Services in Tamworth earlier this month on new rules due to start on August 25.

They said the codes would have permitted the family of Ian Turnbull - who was jailed in 2016 for 35 years for Mr Turner's murder - to legally clear their property near Croppa Creek.