Tourism Ireland may have breached consumer protection rules by commissioning YouTube stars to promote the country without requiring them to disclose clearly that they were engaged in paid-for marketing.

The state agency contracted US bloggers Marko and Alex Ayling, known together as Vagabrothers, to document online their experiences in Sligo, Donegal and Northern Ireland. The brothers’ posts on social media and five of their six YouTube videos, published in November and December and viewed 62,000 times to date, did not indicate that they had been paid to plug Ireland as a tourist destination.

Tourism Ireland said the brothers said “thanks to Tourism Ireland for making this whole trip possible” at the end of their final video, and that the text below the videos stated that Tourism Ireland and Discover Northern Ireland had “made this possible”.

However, this disclaimer is not visible unless the viewer clicks to access the details. Guidelines issued in November by the Advertising Standards Authority for Ireland (ASAI), the industry regulator, state that such disclaimers “should be visible for consumers to see before they interact with the relevant material” and that “a disclaimer below the fold on websites, in terms and conditions, or at the end of the piece is not sufficient”.

The brothers’ posts on social media about their time in Ireland, which did not mention that the trip was sponsored, received thousands of “likes”. In a press release in November announcing the collaboration with Vagabrothers, Tourism Ireland noted that the bloggers’ social media accounts — they have 38,000 followers on Instagram and 27,000 on Facebook — would help to “showcase” Ireland.

“Influencer” marketing via blogs and social media, especially Instagram, has emerged as an important field of advertising, particularly for companies targeting young people, and a lucrative sideline for celebrities.

In Ireland, where the top “influencers” can command lavish gifts and fees of thousands of euros per post, regulation is beginning to tighten.

Scanlon posted photos of places she visited and put up rapturous comments on Twitter and Instagram

The ASAI is investigating three influencers for non-disclosure of alleged marketing communications — the first formal investigations of this kind in Ireland. The ASAI is also assessing whether investigations are warranted in two further cases. Mary Mitchell O’Connor, the enterprise minister, recently confirmed that the Consumer Protection Act 2007, under which it is illegal to use editorial content to promote a product without making it clear if the promotion has been paid for, also applies to social media.

Some Irish influencers, such as the TV presenter Laura Whitmore and the models Pippa O’Connor and Rozanna Purcell, comply with the rules by including the disclaimer “#ad” on paid-for posts.

Failte Ireland, another state tourism agency, provides free holidays to journalists and bloggers in the hope of securing positive social media coverage.

Last week, Angela Scanlon, the Irish BBC presenter, enjoyed a three-day trip to west Cork paid for by Failte Ireland. Scanlon posted photos of places she visited and put up rapturous comments on Twitter and Instagram, as well as links to the Wild Atlantic Way’s social media accounts and to the hashtag #Wild–AtlanticWay. Scanlon did not disclose that the holiday was a gift from Failte Ireland, which runs the Wild Atlantic Way website and brand. She has 41,000 followers on Twitter and 60,000 on Instagram.

Failte Ireland said that, although it had given Scanlon the holiday as part of its “Embrace the Wild Atlantic Way of Life” domestic marketing campaign and had encouraged her to share highlights and photos of her trip on social media, it had not entered into any contract with her or received any guarantee of coverage. That meant her posts were within the ASAI guidelines, which only require a disclosure when the social media user has been paid or has been provided with a product — in this case a free holiday — on the explicit proviso that they give it a positive review.

The spokeswoman said some journalists occasionally did not provide coverage of free trips they had received from Failte Ireland.

“Obviously they don’t get asked again,” she said.

Scanlon’s agent said: “Angela was indeed invited to take part in the Wild Atlantic Way trip and, as a great supporter of Ireland, was delighted to do so. At no point was she paid anything or obliged to post anything on social media. She did so of her own free will, in her own time frame and under her own terms.”

Vagabrothers did not respond to a request for comment.