There is a "maddening" lack of clarity about a new fund to replace EU economic aid for Wales after Brexit, Labour MP Chris Ruane has said.
A full consultation on the details of the new Shared Prosperity Fund was due to be published by UK ministers before the end of 2018.
Opposition parties have expressed concerns about the delay and say details are urgently needed.
A UK government spokesperson said it was intending to consult "shortly".
As one of the poorer parts of the European Union, Wales will have received more than £5bn in so-called structural funds by 2020. That will end when once the UK leaves the EU.
The Conservatives have said the Shared Prosperity Fund is intended to reduce inequalities across the four UK nations.
Theresa May has previously refused to confirm the Welsh Government will control the fund after Brexit.
Chris Ruane, the Labour MP for the Vale of Clwyd and a shadow Wales office minister, says ministers must give more details about the timing and the design of the Shared Prosperity Fund.
"The lack of clarity is absolutely maddening," he said.
"Businesses and other enterprises are tried to operate with their hands tied behind their back as they are unable to make decisions beyond 2020, whilst local government are unable to move infrastructure projects forward because they don't know what support will be available in the future."
"The especially frustrating thing is that this policy is not contingent on the EU or our future relationship, it is an entirely domestic issue and the government could resolve the uncertainty at a stroke if they have the will to do so."
Plaid Cymru MP Ben Lake said the "negligence" shown by the UK government is "astounding".
"This lack of information and forward planning on such an essential funding stream is alarming," added the Ceredigion MP.
EU funding in Wales
Welsh projects supported by European Union funds:
- £3.8bn between 2007-2020 via European Structural Funds investment, helping support employment, training and research
- £957m between 2014-2020 via the Rural Development Programme, supporting businesses, farmers and communities
- £200m a year Common Agricultural Policy, helping 16,000 Welsh farms
- Welsh Government web link explains more about EU funds in Wales
A UK government spokesman said: "The UK Government recognises the importance of reassuring communities on the future of local growth funding once we have left the European Union and providing clarity on the UK Shared Prosperity Fund (UKSPF).
"We have continued to make great progress on the design of the UKSPF over the past year, ahead of the forthcoming consultation.
"Consultation events have been held across the UK, including in Wales, in order to aid policy development. The UKSPF consultation will build on these conversations and we intend to consult shortly."