OK two problems. 24V a.c. isn't actually 24V, it is 24V RMS (route mean square, try a Google) which means that at its peak the input will rise to about 34V, is the PLC input rated for that voltage. Second, the input will actually see 50/60 on's and off's each second. As long as you set the filtering on the input to ignore that cycling then you would be OK, otherwise whatever code you have being operated by the input will be operated 50/60 times per second. Rectifying will fix problem 2 but will still leave you with problem 1.
So the answer to your question is you may be OK but if it was me I would just add a AC relay and let that switch into the PLC.
Bryan