Nov 30 (Reuters) - A number of committed shippers on the Trans Mountain pipeline expansion (TMX) on Thursday wrote to the Canada Energy Regulator to express concerns about the project's request for a variance on a section of the pipeline in British Columbia.

Trans Mountain has asked regulators to be allowed to install smaller diameter pipe in a 2,300-metre (7546-foot) section of the oil pipeline.

Shippers including Canadian Natural Resources Ltd and Suncor Energy said Trans Mountain must bear all responsibility for any "adverse effects or unforeseen impacts" resulting from the variance. (Reporting by Nia Williams; Editing by Sandra Maler)