Coalition 'can't take Wales for granted'.
The Plaid Cymru MP will this morning address a rally against the cuts in Caernarfon, alongside a series of other organisations.
As the Daily Post reported this week, Welsh Secretary Cheryl Gillan insists Wales got a fair deal in the spending review and claims it is a myth that other nations did better.
But Arfon MP Mr Williams will say: "The message we want to get out with today's rally is that the Westminster government cannot keep taking Wales for granted.
"They must listen to the people of Wales and to our democratically-elected Welsh Government.
"Wales has had the worst settlement of all the devolved nations from these budget cuts - and we are simultaneously battling against the worst threat to one of our national institutions, S4C.
"A senior Tory recently claimed that because of the recession we've 'never had it so good', when across Wales people are struggling to make ends meet, facing huge public sector jobs cuts and chronic under investment in our communities. It could not be Plaid's Hywel Williams made plainer how out of touch these people are with the lives of real people."
Other speakers will include the Welsh Language Society, and unions.
Plaid's Hywel Williams Wales