CALGARY, Alberta (Reuters) - Pipeline company TransCanada Corp (>> TransCanada Corporation) will cut 20 percent of its senior management positions as a continuing slump in oil prices has necessitated cost reductions, with further staff cuts possible in the future, a company spokesman said on Thursday.

The company behind the Keystone XL and Energy East pipeline projects said staff were informed Monday about the cuts, which would be implemented over the next several months.

"We don't have an exact number for reductions at the senior level as the process is continuing but when transitions out of the company and retirements are complete, we expect about a 20 per cent reduction in senior leadership positions," spokesman James Millar said in a statement.

"Falling oil prices and the current environment are having a profound impact on our customers and we must do all we can to drive down costs and pursue our projects more efficiently and strategically."

Millar said it would be up to the leaders of business units and other support areas to determine how many employees are affected.

TransCanada laid off 185 people from its major projects division in June, joining several other Calgary-based energy companies, including Suncor Energy Inc (>> Suncor Energy Inc.) and Penn West Petroleum (>> Penn West Petroleum Ltd), that had trimmed staffing levels in order to survive the oil price slump.

U.S. benchmark crude prices have tumbled nearly 60 percent since June 2014, and were last trading at just under $45 a barrel.

(Editing by Chris Reese and Bernadette Baum)

By Nia Williams