Oil exploration company Petroceltic is being sued by its largest shareholder, Worldview Capital Management, which has also called for the resignation of its chief executive Brian O'Cathain.
Petroceltic resolved a dispute with the 27% stake holder in June over a $100m placing of shares.
Worldview had said the placing was an abuse of shareholder rights and urged fellow shareholders to reject it, but eventually reached an agreement with the oil company after winning concessions.
However the Swiss-based investment firm today accused Petroceltic of breaching that agreement by not undertaking a strategic review of the company by a deadline of September 30.
It also said it had started legal proceedings in the High Court and called for the immediate resignation of the CEO.
"It is Worldview's belief that Petroceltic, and in particular Brian O'Cathain, had no intention of complying with the obligation to carry out the review at the time the agreement was entered into," a statement from the company said.
Petroceltic said it had not received notification of any pending litigation.
"The company continues to listen and respond to concerns of its investors, and remains focused on delivering value for all shareholders. Petroceltic will be providing an update on strategy at a planned investor day next month," a spokesman said.
A list of concessions in a statement issued by Petroceltic in June - following the agreement struck with Worldview over the placing - did not include a deadline for a strategic review, but it did say the company expected to hold a capital markets day for investors in the autumn.
It is now scheduled for January 28.