BJP sources said on Saturday a decision on the course of action would be taken in the next few days.
Former finance minister Yashwant Sinha said, "Our only objection is that what is going to be in the Budget has been told to Sonia Gandhi."
"There is a practice in Parliament that anything in the Budget cannot be made public before being presented in the House. What has happened is a clear case of impropriety," he added.
Asked whether the BJP would demand the prime minister's resignation on the issue, he said, "We will raise the issue regarding the prime minister's reply to the letter by the Congress president before the finance minister presents the budget and seek a clarification from him."