The IRS is asking for me to send in hard copies of my W2 forms to verify Social Security tax paid. Don't they already have all that info from my employers?

I submitted my return using TurboTax so I did not send in W-2s, but just got a letter from the IRS asking me to send W-2s in because they need to verify the amount of Social Security Tax paid.  Seems  like an odd request because I thought they would already have that info from what my employer submits directly to the IRS.  Should i send the forms in as requested or could it be a scam?  I tried calling the IRS to see if they sent me a letter but keep getting hung up on.