An unusual provision in Merck & Co Inc's settlement agreement concerning the painkiller Vioxx means many plaintiffs may have little choice but to accept the deal, the Wall Street Journal said Friday in its online edition.

The provision -- agreed to by Merck and the lead lawyers in the case -- requires that if one client of an attorney enrolls in the settlement, then the attorney must recommend the deal to all other clients, according to the Journal.

And if a client decides not to take part in the settlement, then the lawyer -- according to the deal -- must take all necessary steps to withdraw from representing that client, the Journal said.

No one at Merck was immediately available to comment.

Earlier this month Merck agreed to pay $4.85 billion to settle U.S. claims of heart attacks and strokes allegedly linked to Vioxx.

(Reporting by Justin Grant; Editing by Quentin Bryar)