As far as i know there is no innate way to do this, but there are workrounds. The first would be to manually check the task each time you update, and if its on the wrong day giver it a "start on or after" constraint.

Alternatively, you could set up a new calendar with just Mondays as working days, and put a new null milestone in (it can only occur) Link this from task A and to task B, so that it sits between them. This assumes task B is more than a day long- if its one day or less, you could just use the new calendar for ttask B itself.

the problem this could create is that your critical path, if it runs through task B, would be lost.If its non critical no problem, but be aware that this could cause more problems.

Hopefully someone has a beter solutin, but this is theone I would tend to use.