Lecturers at five Welsh universities are taking strike action in a UK-wide dispute over changes to their pensions.
University and College Union (UCU) members at Swansea, Cardiff, Bangor, Trinity St David and Aberystwyth have walked out.
The union said its members were angry about planned changes to two schemes.
The university Employers Pension Forum said it was disappointed by action over "unspecified potential changes" and a "moderate package of reforms".
College and new university lecturers are members of the Teachers' Pensions Scheme (TPS) and have voted for strike action.
Roughly three-quarters of UCU members in the UK who voted - 76% in further education and 72% in higher education - backed the strike action, the union said.
UCU members at older universities are members of a separate scheme, the Universities Superannuation Scheme (USS). Two weeks ago they backed strike action over changes to the scheme which they say will reduce its benefits and increase its costs.
The first walkout over USS changes took place in Scotland on Thursday. Further strike days are planned in Northern Ireland on Monday, while England's members of the USS scheme will take action on Tuesday.
On 24 March, members of the TPS scheme will join members of the USS scheme in a UK-wide walkout.
UCU general secretary Sally Hunt told BBC Radio Wales the employers' position was seen as an "extreme hit" and that "they think they can get away with it and, frankly, they can't which is why strike action is happening".
She added: "We know that students are finding this quite worrying. We're very sorry they have been put in this position.
"The quicker we can resolve this, the quicker we can get back to doing what we should be doing, which is supporting them through their finals."
In response to the UK-wide strike planned for 24 March, an Employers Pension Forum spokesman said on Tuesday: "We are very disappointed that the UCU has decided to take strike action over unspecified potential changes to the TPS and the moderate package of reforms to the USS.
"At present it would seem that the UCU is the only trade union not awaiting the outcome of the current discussions between TUC and the government relating to public sector pension schemes."