UPDATE 2-Four of Canada's biggest banks are key Trans Mountain lenders -filings

(Adds majority owner of Kinder Morgan Canada in fourth paragraph)

CALGARY, Alberta, June 22 (Reuters) - Four of Canada’s biggest banks are the largest providers of C$5.5 billion ($4.16 billion) in credit for Kinder Morgan Canada Ltd’s Trans Mountain pipeline expansion project, the company said in regulatory filings on Thursday.

Along with 20 other banks backing the expansion, they are expected to face increasing pressure from environmental and indigenous activists, who have said they would ask the financial institutions to drop Trans Mountain once they are named.

Royal Bank of Canada, Canadian Imperial Bank of Commerce, Bank of Nova Scotia and Toronto-Dominion Bank provided nearly a third of the credit, according to filings with the U.S. Securities and Exchange Commission.

The four lenders to Kinder Morgan Canada, majority-owned by Kinder Morgan Inc of Houston, did not immediately respond to requests for comment.

Energy infrastructure projects in Canada have faced opposition from environmental groups and aboriginal communities whose land they cross.

Opposition to Trans Mountain’s expansion is set to mount after the effective rise of an unfriendly provincial government last month in Canada’s British Columbia, which the pipeline passes through.

A coalition of more than 20 indigenous and environmental organizations this month called on 28 major banks - including all four of the main lenders - to back away from Trans Mountain.

Jason Opena Disterhoft, senior campaigner for Rainforest Action Network, one of the groups, said the banks have chosen to back the expansion despite being aware of what he says are the environmental impacts.

“We are in communication with those banks,” he said. “We’ll be following up with them and holding them to account.”

One bank targeted by the groups’ letter has since publicly distanced itself from the expansion. ING Groep NV of the Netherlands said last week on Twitter that it is not among the banks funding Trans Mountain.

A bank spokesman said on Thursday it does not lend to projects directly linked to oil sands.

The Trans Mountain expansion almost triples the capacity of the existing pipeline, which is designed to carry crude from Canada’s oil sands to the West Coast.

The expansion has obtained both federal and regulatory approvals and has passed an environmental assessment under British Columbia’s incumbent Liberal Party, which lost its legislative majority in a May 9 election.

The opposition Greens and New Democrats parties, both of which oppose Trans Mountain’s expansion, have sealed a deal to unseat the Liberals. ($1 = 1.3231 Canadian dollars) (Reporting by Ethan Lou; Editing by G Crosse and Lisa Shumaker)