Siliconware Precision Industries (SPIL) has argued that the price offered by Advanced Semiconductor Engineering (ASE) for a further stake in the company is too low.

Citing assessments made by independent accounting firms including Dingshuo and Diwan & Co., SPIL indicated the reasonable transaction price should range from NT$56.33 to NT$68.60 per share. The price proposed by ASE of NT$55 is lower than the suggested price ranges, and therefore is not reasonable, SPIL said.

SPIL also said the new tender offer launched by ASE aiming to boost its stake in SPIL to almost 50% could spark antitrust concerns.

"In view of ASE's tender offer prospectus not disclosing whether ASE has completed a thorough evaluation nor whether ASE has made filings with the competent authorities in foreign countries and jurisdictions, ASE needs to provide more information in order to resolve such doubts," SPIL noted.

In Taiwan, ASE has already filed an application with the local fair trade authority for approval of the investment in SPIL.

Considering antitrust concerns and the "unreasonable" price, SPIL has asked its shareholders to reject ASE's tender offer.

ASE, which in October 2015 acquired a 25% stake in SPIL through an unsolicited tender offer, on December 29 launched a second unsolicited bid for an additional 24.71% stake in the company.