Lawyers acting for Hasler filed a statement of claim in the NSW Supreme Court this week.
Hasler was sacked in September just five months after the Bulldogs announced he had signed a two-year extension to his contract.
In response, club chairman Ray Dib said the club was preparing a legal defence.
"This week the club received court documents filed by Des Hasler's lawyers. The club intends to defend the matter," Dib said in a statement.
Dib claimed at the time the deal was not legally binding.
"Des's current contract expires October 2017," Dib said in September.
"The board has made the decision not to renew that contract and going forward there will be no liabilities for the club for the next two years."
However, the Bulldogs had spruiked Hasler's re-signing in an April 3 press release and press conference.
"Coach Des Hasler will remain with the Canterbury-Bankstown Bulldogs for the next two years after signing a contract extension that will keep him at the club until the end of the 2019 season," the club said in that April statement.
Hasler's claim was filed on Monday and the case is listed for a directions hearing on December 1.