How to force Conda to use gcc found at /usr/bin/gcc?

On Ubuntu 18.04 I run which gcc and the output is as expected.

ubuntu@USER1:~$ which gcc
/usr/bin/gcc

However when I activate my conda environment and run which gcc I get:

(tensorflow_p36) ubuntu@USER1:~$ which gcc
/home/ubuntu/anaconda3/envs/tensorflow_p36/bin/gcc

This location seems strange to me. I wan to use the normal system wide gcc.

I know this is not default behaviour as in my other Ubuntu instance when I run which gcc the output is correct:

(tensorflow_p36) ubuntu@USER2:~$ which gcc
/usr/bin/gcc

How can I get conda to use the default gcc as shown with USER2?

EDIT:

USER1 instance: conda 4.5.12

(tensorflow_p36) ubuntu@USER1:~$ gcc -v
Reading specs from /home/ubuntu/anaconda3/envs/tensorflow_p36/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.8.5/specs
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/home/ubuntu/anaconda3/envs/tensorflow_p36/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.8.5/lto-wrapper
Target: x86_64-unknown-linux-gnu
Thread model: posix 
gcc version 4.8.5 (GCC)

but

ubuntu@USER1:~$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Thread model: posix
gcc version 8.3.0 (Ubuntu 8.3.0-6ubuntu1~18.04.1)