The Japanese company that built corrosion-plagued steam tubes for California’s San Onofre nuclear power plant says it will fight allegations of wrongdoing by the plant’s operator.

Mitsubishi Heavy Industries sent a reply Thursday to a letter from Southern California Edison that accused the company of “gross negligence.” Edison argues that Mitsubishi is liable for costs that could run millions or even billions of dollars.

Mitsubishi’s reply calls the contentions “factually incorrect, legally unsound and inappropriate.” The company says it will defend itself through a dispute resolution process.

Premature wear on the steam tubes shut down the coastal power plant last year and Edison announced last month that it won’t reopen.