* Invesco leaves with immediate effect, CA100+ spokesperson says

* Joins JPMorgan, State Street, Pimco, part of BlackRock

* Invesco says client interests best served by leaving

LONDON, March 1 (Reuters) - Invesco on Friday became the fifth major U.S. investor to exit or scale back their involvement with the Climate Action 100+ coalition of investors, which aims to push highly polluting companies to cut their carbon emissions.

The move follows a decision by the fund arms of JPMorgan and State Street and bond giant Pimco to leave in recent weeks, while BlackRock reduced its involvement with the group.

The decision of Invesco, which manages $1.6 trillion in assets, and the others to leave came as CA100+ gears up to implement Phase 2 of its engagement plan, which would see members put more pressure on companies to cut their emissions.

Coalitions such as CA100+ have been criticised by some U.S. Republican politicians as potentially being in breach of antitrust law, although in a statement last week CA100+ said it was confident this was not the case.

Despite that, and "after careful consideration", Invesco said in a statement it had "decided to withdraw from the Climate Action 100+ initiative as we believe our clients’ interests in this area are better served through our existing investor-led and client-centric issuer engagement approach".

A spokesman for CA100+ said the group continued to have the backing and support of hundreds of investors globally, including asset owners.

"This is supported by the 60 new signatories with approximately $3 trillion in AUM (assets under management) joining since the launch of phase two alone, thereby further highlighting the strong ongoing demand for investor-led climate action." (Reporting by Simon Jessop in London Editing by Greg Roumeliotis, Kirsten Donovan)