"unwelcome effect" is a correct and usable phrase in written English.
You can use it to describe a negative outcome of a situation, such as: "The introduction of new regulations had an unwelcome effect on the company's profitability."
This story may have the unwelcome effect of making children housefly-friendly, but enjoy: it has the wittiest ending – begging the reader not to slam the book shut and make its hero history.
Might the unwelcome effect of such a film not be to turn the site of the Berlin bunker into a type of unhealthy tourist attraction, even for some a pilgrimage site?
He believed that filling the output gap through deficit spending was important, but that a package that was too large could potentially shift fears from the current crisis to the long-term budget deficit, which would have an unwelcome effect on the bond market.
The sale also had the not unwelcome effect of raising £3.2bn for the Treasury's coffers.
Accusing Obama of plagiarism did not brand him a plagiarist, but demonstrated exactly what happened has had another, unexpected and most definitely unwelcome effect on his campaign.
Earlier in April, he even managed to make the prospect of a rise in the minimum wage an issue about Romanian immigrants, suggesting any raise would have the unwelcome effect of attracting more Romanians.
Mr. Newhouse next moves from principle to practice, cataloging the unwelcome effects of Mr. Bush's doctrinal excesses.
In a global world, events in China could have some unwelcome effects on the eurozone.
Plans for redeveloping the City of Newport are having unwelcome effects on Mansion Hill.
However, there are several issues of concern in this sector, including high rates of foreign ownership and control, unwelcome effects on the environment, rapid rates of extraction that may exhaust the reserves, and the widespread but not universal neglect of simple preshipment processing in Australia.
New mobility services have the potential to complement public transit, but they could also lead to worsening traffic congestion, more vehicle accidents, additional air pollution and other unwelcome effects if not managed carefully.
