SNP success could divert money from Wales, Plaid warns
"All the attention and resources" could be diverted to Scotland in the event of SNP gains at the general election, Plaid Cymru has warned.
The party's campaign coordinator Lord Wigley said a "potentially powerful SNP" was already "calling the shots and framing the agenda" for after the poll.
Lord Wigley said a "strong group of Plaid MPs" would be needed to put Wales on an equal footing with Scotland.
He was speaking ahead of Plaid Cymru's election campaign launch on Friday.
The SNP currently has six MPs at Westminster, but recent opinion polls suggest it could make dramatic gains in May.
Lord Wigley said: "We already see how a potentially powerful SNP, with Alex Salmond returning to Westminster, is calling the shots and framing the agenda for the next Parliament.
"We wish them well in standing up for the interests of their country, but we in Wales cannot afford to be left behind in this process."
Responding, SNP election campaign director Angus Robertson told BBC Wales: "SNP MPs will work with our colleagues in Plaid Cymru to help build a progressive alliance at Westminster that will put forward a fairer alternative to austerity and ensure that neither Scotland or Wales can be ignored at Westminster."
Analysis by Nick Servini, BBC Wales political editor
So what exactly is the relationship between Plaid Cymru and the SNP?
The party's press release says Plaid have to make an extra special effort otherwise all the attention and resources will be diverted to Scotland.
And yet Dafydd Wigley gave me the impression at their conference in Caernarfon earlier this month that there was a far more united approach between the two nationalist parties.
He said then: "The SNP have said very generously and constructively that they would be quite prepared to put the needs for Wales to get a new funding formula as part of any packages going forward."
The relationship between Plaid and the SNP is a key one as Plaid have put the possibility of them holding the balance of power in the event of a hung parliament centre stage.