shortest path with constraints that some nodes can not be on the same pth

Given a Graph G, and a pair node s, t.
Need to find a shortest path from s to t.
There is a constraint: some nodes may not appear on the same path.
For example, given a path, s, v1, v2, v3, v4,....vp, t.
It would be not a feasible solution if v2 and v4 can not appear on the same
path.

I would be grateful if some one point to me either an existing efficient
algorithm or some insight on how to find one.

thanks a lot!


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