The phrase "regretful decision" is correct and usable in written English.
You could use it to indicate a decision that was made but is now being regretted. For example: "The mayor made a regretful decision to raise taxes this year."
This is a very regretful decision for me.
"Taking all things into account, mainly the well-being of our employees, the safety of our contractors and in fact our vendors also, we've taken the very regretful decision to move the Nano project out of West Bengal," he said.
In 2012, when a shelter announced its regretful decision to start killing pets, People for the Ethical Treatment of Animals sent them a congratulatory basket of vegan cookies.
As a result, you often make regretful decisions.
There is some relief in learning that some of our regretful purchasing decisions may have been caused by unavoidable mental fatigue, and not a fundamental personality flaw. .
One is tearfully regretful about his decision, the other relieved because he figures that he has a few more years of good health and freedom from worry before he becomes ill.
But he stood firm by his choice, saying, "I'm not regretful of the decision, I think things would have been worse had we not done that".
Chances are, you'll grow up, look back and feel really regretful about your decisions in the past.
The United Nations Human Rights Office for southeast Asia says the court decision was regretful.
His hapless father, regretful of his youthful decision to abandon ship, is striving to connect through phone calls, fried chicken and a surprise visit to make amends before it's too late.
If rather than looking at this decision with regretful eyes I keep this belief alive, I can only continue to feel that I will indeed in the end be successful.
