A strike in Frankfurt will mean that no U-Bahn trains or trams will be running on Wednedsay, 19th March, 2014. A number of bus routes are also affected.
Some of the bus drivers will also be striking on Thursday and Friday.
Oberursel in particular will be affected by the U-Bahn not running. To get to Frankfurt the best alternative will probably be the S-Bahn S5.
What is the reason for the strike? Money?
Yes, although I think some are striking for better working conditions as well.