* Norwegian pension fund KLP considers shareholder proposal

* Fund says Musk underestimates worker dispute

* Tesla has said Swedish conditions already meet demands

* KLP excluded Tesla from its sustainable funds last year

OSLO/STOCKHOLM, April 11 (Reuters) - Tesla investor KLP may ask the automaker's annual general meeting to address CEO Elon Musk's reluctance to engage in collective bargaining, the Norwegian pension fund said on Thursday.

A strike by Tesla mechanics in Sweden, among the country's longest labour disputes, has for months disrupted the automaker's operations and attracted the concern of several Nordic institutional investors.

On Monday, Musk said "the storm had passed on that front". But the strike is continuing and the union leading the action told Reuters this week it may ramp it up.

KLP, Norway's largest pension fund, was a signatory to a December letter sent by Nordic investors expressing their concern about the strike in Sweden and Tesla's reluctance to acknowledge a right to collective bargaining.

"That Elon Musk is saying that the 'storm has passed' is just his way to underestimate the conflict and the issue," Kiran Aziz, KLP's head of responsible investments, told Reuters.

"The conflict is still going and Musk does not really want to understand that collective bargaining is the backbone of the Nordic labour model."

Tesla did not immediately respond to a request for comment. It has previously said its Swedish employees have as good, or better, terms than those the union is demanding.

Aziz said Tesla had not answered the December letter, and KLP was now "trying to figure out how to escalate".

When KLP disagrees with the management of a company in its portfolio, it first tries to establish a dialogue with the company, before moving to outline its expectations to the board, Aziz said.

"The next step with Tesla could be filing a shareholder proposal at its annual general meeting," she said, without elaborating on its contents.

"We will continue to pursue this issue regardless of what Musk thinks so one advice would be that Tesla starts to respond on queries from investors."

KLP holds 900,000 Tesla shares worth some 1.7 billion crowns ($157 million). Last summer it removed Tesla shares from its sustainable funds.

"We did that before the strikes began, because our portfolio managers were seeing that it would come to some controversy," Aziz said. "The Tesla holdings is still in the other funds."

($1 = 10.8039 Norwegian crowns) (Reporting by Gwladys Fouche in Oslo and Marie Mannes in Stockholm; editing by Philippa Fletcher)