Egypt's Muslim Brotherhood opposition group says police detained 23 of its members for campaigning against the country's newly-extended emergency law.
MPs staged noisy protests against renewing the law
"They were arrested at dawn as they were putting up posters and banners denouncing the renewal of the state of emergency," an official said.
Another 25 activists were detained earlier in the week, reports say.
MPs renewed the decades-old emergency law for another two years on Sunday, sparking widespread condemnation.
The law, introduced in 1981, increases powers of arrest and restricts some political activities.
The Brotherhood is officially banned in Egypt, but occupies one fifth of parliamentary seats with MPs elected as independents.
An official with the prosecutor's office quoted by the Associated Press news agency confirmed the arrests.
The US, a key Egyptian ally, said it realised Egypt faced security problems.
But it said it wanted President Hosni Mubarak to honour a pledge to replace the emergency regulation with a law targeting terrorism which at the same time upheld human rights.
"Certainly we would like to see President Mubarak and his parliament follow through on that pledge," US State Department spokesman Sean McCormack said.
"So with respect to this particular action, I can only say we are disappointed."