Can being single be a barrier to career advancement?

I was told that in the corporate world that being single can be a barrier to career advancement.The theory is that married employees have more stability than tbose who are single;therefore,singles will find themselves locked out of the very top executive positions.While I understand that it would be illegal to make an actual rule to that effect within a given company,it exists as an "unwritten rule"that acts as a "glass ceiling "to promotion.Is there any truth to this?