The NUJ strongly condemned Ofcom for putting off the decision.
It claimed STV staff had been overstretched trying to produce its existing news service while they waited for Ofcom to make up its mind.
Scottish organiser Nick McGowan-Lowe said: “Either Ofcom choose to stand by their earlier statement that these proposed changes are ‘the best thing for audiences’, or they listen to the 83% of viewers in the north of Scotland, the leaders of the five main political parties and STV’s own journalists.
“Whichever way they choose to decide, STV’s viewers and journalists deserve to know the decision now and there is no sound reason why this decision should be delayed until after the Scottish elections.”
STV is expected to provide an update on its efforts to make savings and the state of the advertising market when it publishes its annual results on Tuesday.
It is also involved in a dispute with the NUJ and the other main broadcasting union BECTU over a proposed pay freeze.
Both unions are currently holding strike votes. The results of these are due next week.
In January the NUJ held a one day strike over the news cuts and the risk of compulsory redundancies.
STV has been contacted for comment.