Job Elimination - Severance Pay

My company is moving my department to another state. They have gave us a severance benefit, which provides two weeks of severance pay for each completed year of service, up to a maximum of 26 weeks of pay. I started with the company on Jan 26, 1989, I retired on May 31, 2001 and was employed with this company on July 23, 2001. I didn't take any pension pay from my first company. I was only gone for two months. They grandfathered my vacation and sick time from my previous years of service. Which was 20 years in Jan 2009. Now they are saying since I was gone two months,now my beginning date is March 20, 1989 adding the two months I was gone.
In the letter they are saying based upon my tenure with the company of 7 years you are eligible for 14 weeks of severance pay. The reason is they went back to my last hire date July 24, 2001, but in the letter is states completed years of service not my last date of hire. I think I should get 26 weeks of pay.
My question is can they do this and should I contact a lawyer?