Apparently the Bavarian Landtag (Provincial Assembly) rejected the Basic Law (German constitution) in 1949 during ratification. However, the Landtag said it would accept the Basic Law if 2/3 of the states ratified it, which is what happened.
Is it plausible for other German states to reject the Basic Law during ratification? There doesn't seem to be very much information about this on the internet, but it does seem interesting. Alternatively, could we see Bavaria reject the Basic Law and then secede rather than acceding to the other states' ratification?