If you do something under constraint, you do it only because you have been forced to.

They confessed, but only under severe constraint. 他们迫于巨大的压力才说出了真相。

She is not responsible for actions carried out under constraint.

I was under constraint to produce a chapter a week.

I would not want anyone to work for me under constraint.

We joined in willingly with their project, and were under no constraint.