CALGARY, Alberta (Reuters) – Canadian Natural Resources Ltd said on Thursday it is against proposed changes to shipping agreements on Enbridge Inc’s Mainline pipeline system because it does not want to be “held hostage” to one delivery point for its crude.

The Enbridge Mainline system delivers 2.85 million barrels of crude per day from western Canada to the U.S. Midwest, an area known as Padd 2, where it connects to other pipelines stretching across North America.

Enbridge is proposing to shift away from a monthly allocation system to long-term, set-volume contracts. Reuters exclusively reported this week the pipeline company is seeking a minimum eight-year term, raising concerns among small producers that they will lose out to bigger players.

Canadian Natural, Canada’s largest oil and gas