[walk|skate|tread] on thin ice

to be doing something that may get one into serious trouble or danger at any moment

The idiom "walk on thin ice" originates from the literal danger of walking on ice that is not thick enough to support one's weight. It is used figuratively to describe a situation where someone is in a precarious, risky, or delicate position, and any wrong move or action could lead to trouble, harm, or negative consequences.

With the budget cuts looming, any additional spending could be like walking on thin ice.
I don't want to tread on thin ice with my boss by missing the project deadline.
Their relationship is already strained, so discussing that topic would be like skating on thin ice.
Bringing up her past mistake during the meeting would be like treading on thin ice, so it's best to focus on the current issue.
In negotiations, making unreasonable demands can put you on thin ice and jeopardize the deal.