Eldorado Resorts Inc. (ERI) - Get Report is set to unveil an $18 billion merger proposal with Caesars Entertainment Corp.,  (CZR) - Get Report  multiple media outlets reported Sunday, in a move that would challenge industry leaders such as Wynn Resorts (WYNN) - Get Report and MGM Resorts International (MGM) - Get Report .

Reuters first reported that the Eldorado proposal would value Caesars at $13 a share, some 30% higher than its Friday closing price and nearly double where the iconic casino operator's stock was trading at the start of the year. The combined equity value of the two casino operators would be in the region of $12.7 billion, according to figures from the Reuters report, giving the deal an enterprise value of $18 billion once debt from both companies is included.

The possible merger, which could be announced as early as today, comes amid pressure from activist investors Carl Icahn, who boosted his stake in the group to 17.75% earlier this year, to push for either a sale or the merger of the group.

Caesars shares were marked 20.12% higher in pre-market trading Monday, after closing at $9.99 Friday, and indicated to open at $12 each, a move that would extend the stock's year-to-date gain to around 76% as Icahn pushed for changes in the group's senior management team and business structure.

Eldorado shares closed at $51.22 each, a move that would trimmed its year-to-date gain to around 35% and valued the Reno, Nevada-based group at around $4 billion.

Since first revealing his holding in Caesars in March, Icahn has moved to oust former CEO Mark Frissora and replace him with the deal-focused Anthony Rodio, who quickly orchestrated a tie-up with Walt Disney Co. (DIS) - Get Report that will see an ESPN studio erected in the LINQ Hotel & Casino for the production of sports-betting content in the wake of last year's move by the U.S. Supreme Court to overturn a federal on sports wagering.

Caesars has also been linked to a merger with U.K.-based William Hill (WIMHY) , which, according to a piece in last week's Sunday Times newspaper, was preparing a £6 billion tie-up with the Icahn-controlled group under CEO Philip Bowcock.