US President Donald Trump's golf course in Ireland has been given the green light to build a defensive wall, though environmental campaigners said Friday they were planning to launch a challenge.

Initial plans for the sea wall, intended to prevent coastal erosion at his golf resort in Doonbeg on the west coast, involved 200,000 tonnes of rock to build a barrier more than three kilometres long and more than four metres high.

The authorities rejected the proposal but on Thursday gave the go-ahead for a scaled-down project.

The new wall will use 38,000 tonnes of rock and be divided into two sections, totalling one kilometre in length.

However, Tony Lowes, spokesman for Friends of the Irish Environment, told AFP on Friday that they wanted to go before the Planning Appeals Board, calling it a "case of public importance".

He fears that neighbouring beaches and wildlife will be put at risk.

The construction work has the support of the local community, which stands to benefit from 300 jobs linked to the wider Trump golf complex, part of his business empire now being handled by his family during his presidency.

Trump's son Eric said earlier this year that "without a golf course, you don't have a hotel" -- something Lowes described as a "bargaining technique", even though he acknowledged that the money generated by the hotel would be a "big plus" for an economically struggling region.

"We don't have to lose these jobs; we just have to redesign the golf course," he said.

Friends of the Irish Environment is gathering its evidence to present before the Planning Appeals Board before the January 26 deadline.