An Indian-owned contractor has said it plans to sue Macmahon Holdings for blocking its competing bid to buy the WA company's construction business.
Sembawang Engineers and Constructors also called on Leighton Holdings to allow the Singapore-based company to conduct due diligence on the unit.
Biggest shareholder Leighton is not expected to waive an exclusivity period agreed in its $20 million agreement to acquire most of Macmahon's construction projects before Macmahon shareholders vote on the deal next month.
Sembawang - owned by India's Punj Lloyd - has offered to buy the unit outright or match Leighton's deal for an extra $5 million.
Chief executive Richard Grosvenor said Sembawang had instructed its lawyers to file suit against Macmahon because it did not tell the market of his November 26 offer.
Mr Grosvenor said the offer had been followed by a "deafening silence" before Macmahon's announcement of the Leighton deal more than two weeks later.
"To find that an MOU with Leighton, which followed our offer, precludes any other suitor from proceeding with a due diligence process without Leighton's prior consent, leads me to conclude that the interests of the other minority shareholders have been taken hostage," he said.
Rejecting Mr Grosvenor's claims, Macmahon managing director Ross Carroll said no legal action had begun.
"We responded favourably twice to his enquiries about making an equity investment in us," Mr Carroll said. "We also did correspond with him regarding that expression of interest regarding (acquiring) construction. We said we weren't in a position to do a deal with him. For him to say there was no correspondence is not right."
Mr Grosvenor said he expected Leighton under managing director Hamish Tyrwhitt to respect Sembawang's ethical rights by allowing due diligence to proceed.
The ex-Leighton executive also said Mr Tyrwhitt had also shown "character of conscience" by allegedly converting to Islam during his stint in Asia - a possible reference to Mr Tyrwhitt's marriage to Malaysian wife Farina.
A Leighton spokesman said the company had entered into a legally binding agreement with Macmahon. "We continue to take steps with Macmahon to progress it," he said. The spokesman said Mr Tyrwhitt was not religious.