Techniques for controlling data transmission are described. In an aspect, a user equipment (UE) determines whether to send a packet based on available transmit power. The UE determines a first packet size based on the available transmit power and sends a packet of the first packet size if it is equal to or larger than a minimum packet size. The UE sends a packet of a second packet size (e.g., the minimum packet size) if the first packet size is smaller than the minimum packet size and if at least one condition is met, e.g., the available transmit power is greater than a power threshold and the delay of a packet to send is larger than a delay threshold. In another aspect, the UE operates in a discontinuous transmission (DTX) mode and cancels the DTX mode if the delay of a packet to send exceeds a threshold.