The expected merger between Publicis and its competitor Omnicom will effectively topple market leader WPP from the top position.

Publicis will make the merger official on Sunday when it is slated to make a "major corporate announcement."

Although Omnicom is relatively larger compared to the French advertising company, the merger is being billed as a partnership among equals, the Reuters report said. Omnicom is worth US $16.8 billion against Publicis market value of US $16.6 billion.

With the merger, the combined company will be managing assets amounting to US $30 billion and share the year sales estimated to be around US $23 billion.  

However, the announcement perked the interest of anti-trust bodies which are wary of the influence of the combined company with the purse equivalent to a fifth of the total global ad spending annually.

There's also the issue of conflict of interest if the new company are handling the accounts of competing clients, analysts said.