Matt Connolly, founder of Sticky Fingers Street Food in Cardiff, has hired law firm JMW Solicitors, which has launched a judicial review against the devolved power.
A formal notice letter has been sent with a deadline of 14 April for the Government to respond.
First Minister Mark Drakeford has been hesitant to provide a reopening date for indoor hospitality in Wales, but has suggested they could reopen in time for the Spring Bank Holiday at the end of May.
Outdoor hospitality settings in Wales are expected to open on 26 April.
The launch of the legal challenge follows a successful crowdfund by Connolly, in which he raised £5,849 to help cover the costs of the action.
Connolly is asking the Welsh Government for a clear date for indoor hospitality to open and seeking an opening date of 12 April in line with non-essential retail businesses.
If the Welsh Government is not willing to do this, it asks for a clear explanation of its reasons and full disclosure of its evidence used in reaching that decision and assessing the risks associated with indoor hospitality.
“The failure to provide any clarity for the opening of indoor hospitality is a massive blow to the industry - we can’t plan without a date to work toward," says Connolly.
"At the same time, we are seeing other sectors that are arguably riskier opening-up without issue - we just want to be treated fairly. We have invested huge amounts of money and time in making indoor hospitality safe, from PPE and safety screens through to extra staff to manage table service - we believe we should be permitted to open our doors again from 12 April in line with non-essential retail.
"If that isn’t possible, at least let us see the evidence used to make that decision - thousands of livelihoods are at stake.
“It has been an incredibly difficult twelve months for the hospitality industry - the last thing we need is more uncertainty.”
The letter sent to the Welsh government points out the contrast with the approach taken by the government in Westminster, which has provided a clear roadmap in which outdoor hospitality will open from 12 April - along with non-essential retail - followed by indoor hospitality on or after 17 May.
“It is unlawful for the Welsh Government to have failed to provide clarity for the hospitality industry - it’s irrational and will cause further harm to businesses," says Oliver Wright, partner at JMW Solicitors.
"It’s a wholly disproportionate approach when considering the other sectors that have been permitted to open. It’s a decision taken in the absence of any apparent facts or evidence.
"The failure by the Welsh Government to provide a clear date is creating more uncertainty for one of the hardest hit sectors.
"They can’t plan without a date to work towards and a lot of businesses could be forced to close for good. They need to know when staff will be removed from furlough and when rotas can be reintroduced; when to start ordering stock and when they can start taking bookings again.”
JMW is also handling the legal challenge against the delayed reopening of hospitality in England led by Greater Manchester’s night time economy tsar, Sacha Lord.
The team was successful in forcing the Government to abandon its ‘substantial meal’ policy, and this week had its challenge against the decision not to allow indoor hospitality until five weeks after non-essential retail expedited through the courts.