Linq query: Filter out "-" character in field from source via Select statement

My "socialsecuritynumber" contains a "-" character, fx. 123456-8888, that I want to remove before searching for a match.

However, I seem to be doing something wrong. In the “Foreach” it is no problem, but I want to place it in my Select statement.

Hope you can help :-)

            var contactquery = (
                from c in xrm.ContactSet
                join bu in xrm.BusinessUnitSet on c.OwningBusinessUnit.Id equals bu.BusinessUnitId
                where bu.Name == businessunit
                //where c.socialsecuritynumber.Contains(input)            [WORKS]
                //where Char.IsDigit(c.socialsecuritynumber).Contains(input)             [DOES NOT WORK]
                select new { c.ContactId, c.socialsecuritynumber, c.FullName }
            )
            .Distinct()
            .ToList();