Mitt Romney's three-tier marriage proposal which would grant marriage rights to some gay couples has been rejected by gay GOP group Log Cabin Republicans.

The 64-year-old Romney made his proposal during a wide-ranging interview with the Boston Herald's editorial board.

Romney proposed a federal constitutional amendment that would allow gay couples already legally married to remain married but bar future marriages of gay couples.

R. Clarke Cooper, executive director of Log Cabin Republicans, called the proposal unacceptable.

“Governor Romney is contorting himself into a pretzel trying to avoid the simplest solution to a purely political problem. The best way to strengthen all families is to grant equal access to civil marriage for all couples regardless of their orientation,” said Cooper in a statement. “Governor Romney's proposal to create a stratified system is a recipe for legal chaos. It is an offense to the rights of states like New Hampshire that have chosen to legalize marriage equality, and would, for the first time since the Civil War, enshrine second class citizenship in the American Constitution. On the state level, California is already struggling to deal with the fallout of multiple classes of marriage rights imposed by Proposition 8, proving that this system simply doesn't work. Log Cabin Republicans appreciate the governor's efforts to find middle ground, but this is not an acceptable solution.”

Romney's proposed three-tier system is similar to what has already happened in California, where passage of a gay marriage ban, Proposition 8, put an end to the weddings of gay couples, but the state's highest court kept intact the marriages of 18,000 gay couples performed during the brief window when such unions were legal.

Romney's comments come just days after a gay Vietnam veteran asked him his thoughts on Republicans' plans to repeal a gay marriage law in New Hampshire. Romney said he supported the effort to repeal the law. In an interview with MSNBC's Chris Matthews, the veteran, Bob Garon, said Romney “doesn't know about the constitution.”

(Related: Mitt Romney inconsistent on gay rights? Depends on who you ask.)