Oznayim la'Torah: They meant it literally, since the intensification of the already back-breaking work for the slaves and the additional beatings of the officers could well spell death.

Ramban (to 1:10): Bnei Yisrael knew only too well, that the Mitzrim had subjugated them cunningly, gradually, in a way that they would not realize what was happening (see 1:10:1:3*). They said to Moshe, this [demand to leave] will be the last straw! They will accuse us of treason to the crown, and begin to slay Yisrael publicly by the sword, without any more tricks.