An employee of Thailand's state-run electricity authority was killed in an artillery attack on Sunday, prompting an evacuation of dozens of Thai staff working on the project.
In May a Thai geologist working on the project was killed after stepping on a landmine.
Myanmar's state-run New Light of Myanmar newspaper has blamed Sunday attack on the rebel Karen National Union.
Locals have criticized the $1bn Salween dam project as threatening the livelihoods of millions of people who live along the river.
The project has also been criticised by environmentalists, who say the dam will destroy a remote and ecologically rich region.
Plans have been drawn up for as many as 18 dams and diversions along the length of the Salween river - 13 in China and five where the river runs inside Myanmar or forms its frontier with Thailand.