BA cabin crew have a history of taking sick days rather than going on strike. It could be argued that if you are absenting yourself from work on a strike day and you are not genuinely sick then you are either a: taking unofficial industrial action or b: putting yourself in breach of contract by defrauding the company. Both are actions that can lead to dismissal.
BA have been pretty even handed about this as all they chose to do was to warn the crew that if they were sick on strike days they would be treated as strikers unless they could prove that they were genuinely sick. For those that were sick this should present an obstacle, all they have to do is get a sick note. Having been warned before hand that this would be a requirement only those who were not really sick or were too lazy or stupid to get a sick note will be on the wrong end of this issue.
A question for all the lawyers out there, is a sickness policy part of your contract and therefore needs agreement to vary, or is it a company policy that can be varied by the company with prior notice?