Venezuelan President Hugo Chavez has set a deadline for Brazil and Paraguay to back his country's membership of South American trading bloc Mercosur.
Mr Chavez issued the ultimatum during a televised speech
Mr Chavez warned the two he would ditch the membership request if they failed to back it within three months.
Brazilian senator Sergio Zambiassi has warned its lawmakers are unlikely to approve the request before September.
Experts say this latest move puts further pressure on already strained relations in Mercosur.
"We are making an effort to speed it up ... but I cannot guarantee that it will be approved before September," Senator Zambiassi said.
Venezuela's membership has already been approved by the leaders of all five member states and by the Uruguayan, Argentine and Venezuelan parliaments.
However, it must still be ratified by the Brazilian and Paraguayan legislatures.
Relations between Brazil and Venezuela have been tense for some weeks.
They deteriorated further after the Brazilian Senate called on Mr Chavez to revise his decision not to renew the licence for opposition TV channel Radio Caracas Television (RCTV).
Mr Chavez denounced Brazil as a "parrot" of the US for criticising the decision.
Brazil has called for President Chavez to apologise for the comments, something he has so far refused to do.