trouble is brewing

There is difficulty, danger, or unrest fermenting or expected to arise in the future. According to many inside the region, trouble is brewing among working-class voters who felt betrayed by the recent legislative change. We sensed that trouble was brewing, so we got out of the bar before the fight broke out.

Trouble is brewing.

and There is trouble brewing.

Fig. Trouble is developing. Trouble's brewing at the office. I have to get there early tomorrow. There is trouble brewing in the government. The prime minister may resign.