Germany's parliament approved the nation's rescue package for Greece on Friday, while opposition voices are loud in the country.

The Bundestag, or the lower house of parliament approved the bill with 390 voting in favour, 72 against, and 139 abstaining. Later, the upper house, the Bundesrat, passed the bill smoothly as the coalition government enjoys a majority there.

On Monday, German Chancellor Angela Merkel's government approved a rescue package of 22.4 billion euros (28.5 billion U.S. dollars) for Greece over the next three years, as part of a 110 billion-euro international rescue plan backed by eurozone members and the International Monetary Fund.

The approval of the bill provides legislative support for Merkel, who will attend the summit for eurozone nations in Brussels on Friday evening to discuss the details of the international rescue package.

Merkel praised the vote as an important decision to ensure " greater security for euro for our citizens," after the approval.

She also reiterated the importance for Greece to strictly implement the austerity plan it promised , saying the bailout plan "will only be effective in combination with the ambitious Greek austerity program."

Although the bill has been approved, the opposition voices are still quite loud in the country, which may affect Merkel's later actions.

The country's most widely-read newspaper, Bild, has criticized the rescue plan for violating the article of the Lisbon Treaty which forbids one member state from assuming the liabilities of another.

Opinion polls have shown a majority of Germans oppose this largest bailout plan in euro history, which may cause Merkel's coalition government to lose a very important upcoming local state election.

On Sunday the state North Rhine-Westphalia will hold its legislative election. It is the most populous state in Germany, which is governed by the same coalition CDU-FDP as the federal government.

The state has 13.5 million voters, which have frequently set the future course for German federal politics. The latest survey showed 56 percent of voters thought aiding Greece was wrong.

If the state's current local government failed on Sunday, Merkel's government will lose its majority in the Bundesrat.

The major opposition party, the Social Democrats (SPD) also showed their opposition to the bill Friday, as most of them chose abstaining the bill as their leader Frank-Walter Steinmeier said Thursday.

While the parliament approved the package, five German academics, including eurosceptic economist Joachim Starbatty, on Friday filed a lawsuit against it at the Federal Constitutional Court in Karlsruhe, Germany's highest court.

They said, no German loans should flow to the debt-laden country before a ruling comes out.