Nexstar hasn’t persuaded Media General directors to accept its merger proposal, potentially creating the nation’s No. 2 TV station owner. Now it wants Media General shareholders to get involved.

The companies have reached an “impasse,” Nexstar says this morning, after the broadcaster raised its cash and stock offer to $16.31 per share, equal to about $2.1 billion.  Media General wants $18.60.

Nexstar’s latest offer is “at the limits of reasonable [earnings] multiples” for Media General, Nexstar CEO Perry Sook says. And it could vanish soon.

“Given factors such as the current interest rate environment and the impending commencement of high levels of political advertising, time is of the essence and further delays in reaching reasonable terms for a transaction could impact the value creation we outlined at the time we announced our original proposal,” Sook says.

Media General shareholders, he adds, “will be disappointed with their Board’s unreasonable negotiating position given the immediate and long-term strategic and economic benefits a combination with Nexstar would provide.”

Nexstar made an unsolicited bid for Media General in September after the broadcaster agreed to pay $2.4 billion in cash and stock for Meredith, creating the No. 3 station owner with magazines led by Better Homes And Gardens, Allrecipes, Parents, Family Circle, and Shape.

Nexstar’s current offer consists of $11.00 per share in cash — or $10.54 if Media General has to pay a $60 million break-up fee by scrapping its deal with Meredith. In addition, Nexstar will kick in 0.1024 of one of its shares for each Media General share.

Nexstar adds that it would enable Media General shareholders to benefit from the sale of its airwave spectrum. The FCC wants to auction to wireless broadband providers some of the spectrum that broadcasters currently use, and share the proceeds with station owners.

Wells Fargo Securities’ Marci Ryvicker says her hunch is that the “saga is not totally over” with the companies “negotiating in the press.” If she’s right, then they may end up somewhere between the $16.31 Nexstar is offering and the $18.60 Media General wants.

As for Meredith, it “might somehow try to squeeze its way in, as a few investors have suggested (but which many just don’t believe).”

Media General shares are up nearly 3% in premarket trading while Nexstar and Meredith are flat.