ESPN NFL Insider Adam Schefter first reported the news.
"Logan Mankins is a tremendous player. He has been a fixture on our offensive line since we drafted him in the first round of the 2005 NFL draft and he remains an important part of our future plans," the team said in a statement. "Unfortunately, we have not been able to reach a long-term agreement, despite many attempts and proposals by both sides. That remains our objective in utilizing the franchise designation and we are hopeful that Logan will be a Patriot for many years to come."
Mankins is the first player to be designated a team's franchise player this offseason. The franchise tag essentially binds Mankins to the Patriots for one year.
The projected contract for a franchised offensive lineman is $10.1 million, down from $10.7 million last season. That salary would be guaranteed once Mankins signed the tender offer.
The Patriots used the non-exclusive tag, according to a source, meaning Mankins can negotiate with other teams and sign an offer sheet. However, that other team would need to forfeit two first-round draft choices to the Patriots, according to the current rules. It is possible that the Patriots would accept less in the form of a trade, assuming they were willing to deal Mankins.
At the Pro Bowl last month, Mankins told the Boston Herald that he wouldn't be happy with the franchise tag. His hope is for a long-term contract that would include more guaranteed money up-front.
Still, the $10.1 million makes it a less bitter pill for Mankins to swallow, as it is more than he has earned in his first six seasons in the NFL.
For the Patriots, the franchise tag protects one of their top assets.
"Logan Mankins is one of the best players on the team," owner Robert Kraft said Feb. 4 at the Super Bowl. "I hope he's with us for a long-term and we're going to try to do whatever we have to do to make sure that happens."
One factor that clouds the future with Mankins and the franchise tag is the NFL's uncertain labor forecast. Owners believe they can use the franchise tag, while the NFL Players Association believes the tag cannot be used because the collective bargaining agreement doesn't extend into the 2011 season.
One of the key considerations with all tagged players is what owners decide when the collective bargaining agreement expires March 4.
If owners lock players out, Mankins could pursue the matter legally by arguing that he can't be restricted with the tag when players are locked out. Some with ties to the NFL Players Association believe Mankins would have a strong case in that scenario.
If owners don't lock players out, Mankins would remain in limbo until a new collective bargaining agreement is reached.
It's possible that teams will eventually be allowed to assign players the franchise tag as part of a new collective bargaining agreement. There is also the possibility that Mankins becomes a free agent if the franchise tag is not part of a new collective bargaining agreement.
Mankins, 28, was a first-round draft pick of the Patriots in 2005. He has been to three Pro Bowls, including this year.
Mankins and the Patriots were at odds last summer, when Mankins said he hoped to be traded because of the slow pace of negotiations on a contract extension.
Mankins was a restricted free agent -- a result of the NFL's going from a salary-cap system to an uncapped year -- but did not sign his $3.26 million tender.
That led to an extended standoff, with Mankins not reporting until the eighth game of the season. The Patriots sliced his tender to $1.54 million, which was prorated over the final nine games of the season.
In an interview with ESPNBoston.com in June, Mankins explained his stance.
"After the 2008 season, me and my agent approached the Patriots about an extension and I was told that Mr. Kraft did not want to do an extension because of the [uncertain collective bargaining agreement]," he said at the time. "I was asked to play '09 out, and that they would address the contract during the uncapped year. I'm a team player, I took them at their word, and I felt I played out an undervalued contract.
"That's the big thing. Right now, this is about principle with me and keeping your word and how you treat people. This is what I thought the foundation of the Patriots was built on. Apparently, I was wrong. Growing up, I was taught a man's word is his bond. Obviously this isn't the case with the Patriots."
Mankins put those feelings aside when he returned to the team Nov. 2, saying his focus was solely on football and helping the Patriots win.
Yet in an interview with the Boston Herald last month at the Pro Bowl, Mankins explained that it was now time to focus on his contract.
"I enjoyed playing there,'' Mankins said of New England. "The season's over. Now it's business time."
Mike Reiss covers the Patriots for ESPNBoston.com. Adam Schefter is ESPN's NFL Insider.