O'Shea Partners, a boutique that disbanded when its lawyers joined Boies Schiller Flexner and then Cadwalader Wickersham & Taft, has been sued by its former client, Madison Equities, for allegedly "fraudulently" padding its legal bills.

The allegations come amid a long-running dispute between O'Shea Partners and Madison Equities, a real estate development company. O'Shea Partners sued Madison Equities in 2016, alleging Madison owed hundreds of thousands of dollars in legal fees. Madison and its principal, Robert Gladstone, have sought a declaration that they owe nothing, plus another $600,000 in refunds.

The O'Shea firm was helmed by Sean O'Shea, who moved with his colleagues to Boies Schiller in 2016 and then to Cadwalader earlier this year.

In a new suit filed Monday in Manhattan Supreme Court, Madison Equities and Gladstone sued the boutique, seeking $900,000 under five causes of action, all for variations of breach of contract. The complaint states in a footnote that it was filed "solely to protect and preserve Madison and Gladstone's rights" if they aren't allowed to amend their counterclaims in the suit O'Shea Partners filed against them in 2016.

Madison Equities challenged a variety of the boutique's fees, from $306,000 to prepare for an appellate court argument to $4,417 to file a stipulation adjourning oral argument. The fees date from 2013 to 2016, when O'Shea Partners was representing Madison Equities in a dispute with Courtyard by Marriott, which ran a hotel in one of its properties.

In a Tuesday interview, O'Shea and his partner Michael Petrella—also now at Cadwalader—pushed back against the allegations, saying Madison and principal Gladstone have shirked their bills at several law firms and were simply trying a new strategy.

"This guy runs around town hiring lawyers, promising to pay and then breaching those promises," said O'Shea, who called Gladstone's new lawyers at Akabas & Sproule "the latest entry and probably will be his latest victim."

David Bamberger, who is of counsel at Akabas and represents Madison and its principal, declined to comment.