The unions have nothing to do with code restictions. They may limit the
materials that they will allow their members to install (back in the 70's,
even though NoHub cast iron was code approved, the local here would only
allow the plumbers to install service weight), but, generally, they have no
control over codes.
Also, your comments "cuts into a plumbers profits don't ya know" and "just a
profit issue with plumbers is all', are rediculous statements. You're mixing
up the union (employees) with the contractors (employers).
Contractors must use whatever code approved materials and methods are
available to them in order to REDUCE the cost of jobs so that they will be
competetive. Even with today's building boom, the profits are less than they
were because the "burden" (insurance, overhead, gas prices, etc) are out of
control and whatever "profit" is left over at the end of a job gets eaten up
by the overhead.